System and Method for Communications Beam Recovery

ABSTRACT

A method for operating a user equipment includes monitoring a first set of reference signals of a first reference signal type transmitted by an access node, each reference signal in the first set of reference signals having a quasi-co-located (QCLed) or spatially similar relationship with a different subset of reference signals of a second set of reference signals of a second reference signal type, identifying a second reference signal from the second set of reference signals as a candidate beam, identifying a first reference signal of the first set of reference signals that is QCLed or spatially similar with the second reference signal, and transmitting a preamble sequence on a random access channel resource that is associated with the first reference signal of the first set of reference signals, thereby identifying the candidate beam for communications at the access node.

This application claims the benefit of U.S. Provisional Application No.62/479,965, filed on Mar. 31, 2017, entitled “Systems and Methods forBeam Recovery and Resource Allocation,” U.S. Provisional Application No.62/521,110, filed on Jun. 16, 2017, entitled “System and Method forCommunications Beam Recovery,” U.S. Provisional Application No.62/544,420, filed on Aug. 11, 2017, entitled “System and Method forCommunications Beam Recovery,” and U.S. Provisional Application No.62/581,314, filed on Nov. 3, 2017, entitled “System and Methods forCommunications Beam Recovery,” which applications are herebyincorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates generally to a system and method fordigital communications, and, in particular embodiments, to a system andmethod for communications beam recovery.

BACKGROUND

One possible deployment scenario for fifth generation (5G) New Radio(NR) system architecture uses high frequency (HF) (6 gigahertz (GHz) andabove, such as millimeter wavelength (mmWave)) operating frequencies toexploit greater available bandwidth and less interference than what isavailable at the congested lower frequencies (below 6 GHz). However,pathloss is a significant issue in HF. Beamforming may be used toovercome the high pathloss issue in HF.

Under certain conditions, a user equipment (UE) device may detect thatall existing communications beam between an evolved NodeB (eNB) and theUE are not working as expected (i.e., there is a beam failure and/orloss) and there is a need to recover from this condition.

Therefore, there is a need for mechanisms supporting communications beamrecovery.

SUMMARY

Example embodiments provide a system and method for communications beamrecovery.

In accordance with an example embodiment, a method for operating a userequipment (UE) is provided. The method includes monitoring, by the UE, afirst set of reference signals of a first reference signal typetransmitted by an access node, each reference signal in the first set ofreference signals having a quasi-co-located (QCLed) or spatially similarrelationship with a different subset of reference signals of a secondset of reference signals of a second reference signal type, identifying,by the UE, a second reference signal from the second set of referencesignals as a candidate beam, identifying, by the UE, a first referencesignal of the first set of reference signals that is QCLed or spatiallysimilar with the second reference signal, and transmitting, by the UE tothe access node, a preamble sequence on a random access channel resourcethat is associated with the first reference signal of the first set ofreference signals, thereby identifying the candidate beam forcommunications at the access node.

Optionally, in any of the preceding embodiments, an embodiment whereinthe first set of reference signals comprises a set of synchronizationsignals (SSs), and wherein the second set of reference signals comprisesa set of channel state information reference signals (CSI-RSs).

Optionally, in any of the preceding embodiments, an embodiment whereinfirst set of reference signals comprises cell specific referencesignals.

Optionally, in any of the preceding embodiments, an embodiment whereinthe second set of reference signals comprises UE specific referencesignals.

Optionally, in any of the preceding embodiments, an embodiment furthercomprising receiving, by the UE, information about the QCLed orspatially similar relationship between the first set of referencesignals and the second set of reference signals in at least one of aradio resource control (RRC) message, a medium access control (MAC)control element (CE) (MAC-CE) message, or a downlink control indicator(DCI) message.

Optionally, in any of the preceding embodiments, an embodiment whereinthe random access channel resource is selected from a plurality ofrandom channel access resources in accordance with the first referencesignal.

Optionally, in any of the preceding embodiments, an embodiment whereinat least one of a time location of the random access channel resource, afrequency location of the random access channel resource, or a preamblesequence information related to the random access channel resource isselected in accordance with the first reference signal.

Optionally, in any of the preceding embodiments, an embodiment whereinthe at least one of the time location of the random access channelresource, the frequency location of the random access channel resource,or the preamble sequence information related to the random accesschannel resource is received in at least one of a RRC message, a MAC-CEmessage, or a DCI message.

In accordance with an example embodiment, a method for operating anaccess node is provided. The method includes sending, by the access nodeto a UE, first information about a QCLed or spatially similarrelationship between each reference signal in a first set of referencesignals of a first reference signal type and a different subset ofreference signals of a second set of reference signals of a secondreference signal type, sending, by the access node to the UE, secondinformation specifying a random access channel resource of a pluralityof random access channel resources to use when a reference signal fromthe second set of reference signals is identified as a candidate beam,and receiving, by the access node from the UE, a preamble sequence onthe random access channel resource, thereby identifying the candidatebeam.

Optionally, in any of the preceding embodiments, an embodiment furthercomprising assigning, by the access node, the random access channelresource or the preamble sequence to the UE.

Optionally, in any of the preceding embodiments, an embodiment whereinthe first set of reference signals of the first reference signal typecomprises a set of synchronization signals (SSs), and wherein the secondset of reference signals of the second reference signal type comprises aset of CSI-RSs)

Optionally, in any of the preceding embodiments, an embodiment whereinthe first information is sent in at least one of a first RRC message, afirst MAC-CE message, or a first DCI message, and wherein the secondinformation is sent in at least one of a second RRC message, a secondMAC-CE message, or a second DCI message.

In accordance with an example embodiment, a UE is provided. The UEincludes a memory storage comprising instructions, and one or moreprocessors in communication with the memory storage. The one or moreprocessors execute the instructions to monitor a first set of referencesignals of a first reference signal type transmitted by an access node,each reference signal in the first set of reference signals having aQCLed or spatially similar relationship with a different subset ofreference signals of a second set of reference signals of a secondreference signal type, identify a second reference signal from thesecond set of reference signals as a candidate beam, identify a firstreference signal of the first set of reference signals that is QCLed orspatially similar with the second reference signal, and transmit, to theaccess node, a preamble sequence on a random access channel resourcethat is associated with the first reference signal of the first set ofreference signals, thereby identifying the candidate beam forcommunications at the access node.

Optionally, in any of the preceding embodiments, an embodiment whereinthe first set of reference signals comprises a set of SSs, and whereinthe second set of reference signals comprises a set of CSI-RSs.

Optionally, in any of the preceding embodiments, an embodiment whereinthe one or more processors further execute instructions to receiveinformation about the QCLed or spatially similar relationship betweenthe first set of reference signals and the second set of referencesignals in at least one of a RRC message, a MAC-CE message, or a DCImessage.

Optionally, in any of the preceding embodiments, an embodiment whereinthe one or more processors further execute instructions to select therandom access channel resource from a plurality of random access channelresources in accordance with the first reference signal.

Optionally, in any of the preceding embodiments, an embodiment whereinthe one or more processors further execute instructions to select atleast one of a time location of the random access channel resource, afrequency location of the random access channel resource, or a preamblesequence information related to the random access channel resource.

In accordance with an example embodiment, an access node is provided.The access node includes a memory storage comprising instructions, andone or more processors in communication with the memory storage. The oneor more processors execute the instructions to send, to a UE, firstinformation about a QCLed or spatially similar relationship between eachreference signal in a first set of reference signals of a firstreference signal type and a different subset of reference signals of asecond set of reference signals of a second reference signal type, send,to the UE, second information specifying a random access channelresource of a plurality of random access channel resources to use when areference signal from the second set of reference signals is identifiedas a candidate beam, and receive, from the UE, a preamble sequence onthe random access channel resource, thereby identifying the candidatebeam.

Optionally, in any of the preceding embodiments, an embodiment whereinthe one or more processors further execute instructions to assign therandom access channel resource or the preamble sequence to the UE.

Optionally, in any of the preceding embodiments, an embodiment whereinthe first information is sent in at least one of a first RRC message, afirst MAC-CE message, or a first DCI message, and wherein the secondinformation is sent in at least one of a second RRC message, a secondMAC-CE, or a second DCI message.

In accordance with an example embodiment, a method for operating anaccess node is provided. The method includes generating, by the accessnode, a configuration message including information specifying a set ofreference signals of a first reference signal type and a set ofreference signals of a second reference signal type used to identify anew beam, and information specifying random access channel resourcesallocated for transmitting preamble sequences, wherein each randomaccess channel resource is associated with a reference signal of thefirst reference signal type, sending, by the access node to one or moreuser equipments (UEs), the configuration message, receiving, by theaccess node from a UE, a preamble sequence on one of the random accesschannel resources, and determining, by the access node, an identity ofthe UE in accordance with the preamble sequence and the one of therandom access channel resources.

Optionally, in any of the preceding embodiments, an embodiment whereineach reference signal in the first set of reference signals having aquasi-co-located (QCLed) or spatially similar relationship with adifferent subset of reference signals of the second set of referencesignals of the second reference signal type.

Optionally, in any of the preceding embodiments, an embodiment whereinthe configuration message is sent on at least one of a radio resourcecontrol (RRC) message, a medium access control (MAC) control element(CE) (MAC-CE) message, or a downlink control indicator (DCI) message.

Optionally, in any of the preceding embodiments, an embodiment whereinthe set of reference signals of the first type comprises a set ofsynchronization signals (SSs).

Optionally, in any of the preceding embodiments, an embodiment whereinthe set of reference signals of the second type comprises a set ofchannel state information reference signals (CSI-RSs).

Optionally, in any of the preceding embodiments, an embodiment whereinthe random access channel resources comprise physical random accesschannel (PRACH) resources.

Optionally, in any of the preceding embodiments, an embodiment whereineach random access channel resource is also associated with a referencesignal of the second reference signal type.

Optionally, in any of the preceding embodiments, an embodiment whereinthe configuration message further comprises at least one of: timelocation information related to a first random access channel resource,frequency location information related to the first random accesschannel resource, preamble sequence information related to the firstrandom access channel resource, or a first association between a firstreference signal index and the first random access channel resource.

Optionally, in any of the preceding embodiments, an embodiment whereinthe configuration message further comprises at least one of: timelocation information related to a second random access channel resource,frequency location information related to the second random accesschannel resource, preamble sequence information related to the secondrandom access channel resource, or a second association between a secondreference signal index and the second random access channel resource.

Optionally, in any of the preceding embodiments, an embodiment furtherincludes determining, by the access node, an index of an identifiedreference signal as a first reference signal index when the preamblesequence is received on a first random access channel resource, anddetermining, by the access node, the index of the identified referencesignal as a second reference signal index when the preamble sequence isreceived on a second random access channel resource.

Optionally, in any of the preceding embodiments, an embodiment furtherincludes sending, by the access node to the UE, a beam failure recoveryresponse on a control channel.

Optionally, in any of the preceding embodiments, an embodiment whereinthe control channel comprises a physical downlink control channel(PDCCH).

Optionally, in any of the preceding embodiments, an embodiment whereinthe control channel is spatially QCLed with the identified referencesignal.

In accordance with an example embodiment, an access node is provided.The access node includes a memory storage comprising instructions, andone or more processors in communication with the memory storage. The oneor more processors execute the instructions to generate a configurationmessage including information specifying a set of reference signals of afirst reference signal type and a set of reference signals of a secondreference signal type used to identify a candidate beam, and informationspecifying random access channel resources allocated for transmittingpreamble sequences, wherein each random access channel resource isassociated with a reference signal of the first reference signal type,send the configuration message to one or more UEs, receive, from a UE, apreamble sequence on one of the random access channel resources, anddetermine an identity of the UE in accordance with the preamble sequenceand the one of the random access channel resources.

Optionally, in any of the preceding embodiments, an embodiment whereinthe configuration message is sent on at least one of a RRC message, aMAC-CE message, or a DCI message.

Optionally, in any of the preceding embodiments, an embodiment whereinthe one or more processors further execute instructions to determine anindex of an identified reference signal as a first reference signalindex when the preamble sequence is received on a first random accesschannel resource, and determine the index of the identified referencesignal as a second reference signal index when the preamble sequence isreceived on a second random access channel resource.

Optionally, in any of the preceding embodiments, an embodiment whereinthe one or more processors further execute instructions to send, to theUE, a beam failure recovery response on a control channel.

Optionally, in any of the preceding embodiments, an embodiment whereineach reference signal in the first set of reference signals having aQCLed or spatially similar relationship with a different subset ofreference signals of the second set of reference signals of the secondreference signal type.

In accordance with an example embodiment, a non-transitorycomputer-readable medium is provided. The non-transitorycomputer-readable medium stores programming for execution by one or moreprocessors to generate a configuration message including informationspecifying a set of reference signals of a first reference signal typeand a set of reference signals of a second reference signal type used toidentify a candidate beam, and information specifying random accesschannel resources allocated for transmitting preamble sequences, whereineach random access channel resource is associated with a referencesignal of the first reference signal type, send the configurationmessage to one or more UEs, receive, from a UE, a preamble sequence onone of the random access channel resources, and determine an identity ofthe UE in accordance with the preamble sequence and the one of therandom access channel resources.

Optionally, in any of the preceding embodiments, an embodiment whereinthe one or more processors further execute instructions to determine anindex of an identified reference signal as a first reference signalindex when the preamble sequence is received on a first random accesschannel resource, and determine the index of the identified referencesignal as a second reference signal index when the preamble sequence isreceived on a second random access channel resource.

Optionally, in any of the preceding embodiments, an embodiment whereinthe one or more processors further execute instructions to send, to theUE, a beam failure recovery response on a control channel.

In accordance with an example embodiment, a method for operating a UE isprovided. The method includes determining, by the UE, a first identifierof a first reference signal resource associated with a first referencesignal type transmitted by an access node, determining, by the UE, asecond identifier of a second reference signal resource associated witha second reference signal type transmitted by the access node, sending,by the UE, a beam failure recovery request message including a sequenceon a beam failure random access channel (BRACH) resource identified inaccordance with at least one of the first identifier or the secondidentifier, and receiving, by the UE, a beam failure recovery responsemessage.

Optionally, in any of the preceding embodiments, an embodiment whereinthe method further comprises sending, by the UE, recovery information,and monitoring, by the UE, for a downlink control channel.

Optionally, in any of the preceding embodiments, an embodiment whereinthe recovery information comprises the first identifier.

Optionally, in any of the preceding embodiments, an embodiment whereinthe recovery information comprises at least one of the second identifieror an intra-group identifier identifying a third reference signalresource out of a group of first reference signal resources that arespatially QCL with the second reference signal resource identified bythe second identifier.

Optionally, in any of the preceding embodiments, an embodiment whereinthe beam failure recovery response message comprises a transmissiongrant, and wherein the recovery information is transmitted in accordancewith the transmission grant.

Optionally, in any of the preceding embodiments, an embodiment whereinthe method further comprises receiving, by the UE, a configuration ofthe sequence from the access node.

Optionally, in any of the preceding embodiments, an embodiment whereinthe configured sequence from the access node is different for differentUEs.

Optionally, in any of the preceding embodiments, an embodiment whereinthe method further comprises receiving, by the UE, an associationmessage with information about at least one of associations between oneor more reference signal resources and one or more BRACH resources,associations between the one or more reference signal resources and oneor more BRACH response resources, or associations between the one ormore BRACH resources and the one or more BRACH response resources.

Optionally, in any of the preceding embodiments, an embodiment whereinthe association message conveys information about a known relationship,in terms of time and/or frequency positions, of a first resource typerelative to a second resource type.

Optionally, in any of the preceding embodiments, an embodiment whereinthe BRACH resource is further identified in accordance with theassociation message.

Optionally, in any of the preceding embodiments, an embodiment whereinthe method further comprises receiving, by the UE, first quasico-located (QCL) information associated with a first reference signal ofthe first reference signal type and more than one reference signals ofthe second reference signal type, and/or second QCL informationassociated with one reference signal of the second reference signal typeand more than one reference signals of the first reference signal type.

Optionally, in any of the preceding embodiments, an embodiment whereinthe second identifier of the second reference signal resource associatedwith the second reference signal type is determined in accordance withthe first QCL information and/or the second QCL information.

Optionally, in any of the preceding embodiments, an embodiment whereinthe second identifier of the second reference signal resource associatedwith the second reference signal type is determined by monitoring secondreference signal resources associated with the second reference signaltype.

Optionally, in any of the preceding embodiments, an embodiment whereinthe first identifier of the first reference signal resource associatedwith the first reference signal type is determined by monitoring firstreference signal resources associated with the first reference signaltype.

Optionally, in any of the preceding embodiments, an embodiment wherein afirst time and/or frequency position associated with the beam failurerecovery response message is determined in accordance with a second timeand/or frequency position of a resource conveying the beam failurerecovery request message and an association message conveying at leastone of associations between one or more reference signal resources andone or more BRACH resources, or associations between one or morereference signal resources and one or more BRACH response resources.

Optionally, in any of the preceding embodiments, an embodiment wherein athird time and/or frequency position of a resource conveying the beamfailure recovery request message is determined in accordance with afourth time and/or frequency position of at least one of the firstreference signal resource associated with a first reference signal typeor the second reference signal resource associated with a secondreference signal type.

Optionally, in any of the preceding embodiments, an embodiment whereinthe first reference signal comprises a channel state informationreference signal (CSI-RS) and the second reference signal comprises awideband reference signal (WBRS).

Optionally, in any of the preceding embodiments, an embodiment whereinthe WBRS comprises at least one of synchronization signals (SS), widebeam channel state information reference signals (WB CSI-RS), broad-beamchannel state information reference signals (CSI-RS), SS-mimickingCSI-RS, cell-specific CSI-RS, group CSI-RS, or common CSI-RS.

Optionally, in any of the preceding embodiments, an embodiment whereinthe CSI-RS comprises at least one of narrow beam CSI-RS or UE-specificCSI-RS.

Optionally, in any of the preceding embodiments, an embodiment wherein afifth time and/or frequency position of the BRACH resource conveying thesequence is different from a sixth time and/or frequency position of arandom access channel (RACH) used for initial access purposes.

Optionally, in any of the preceding embodiments, an embodiment whereinthe second identifier is not explicitly transmitted by UE.

Optionally, in any of the preceding embodiments, an embodiment whereinthe second identifier is determined by the access node implicitly inaccordance with time and/or frequency positions of the BRACH resourceconveying the sequence.

Optionally, in any of the preceding embodiments, an embodiment wherein adownlink control channel signal is spatial QCL with the first referencesignal resource identified by the first identifier.

In accordance with an example embodiment, a method for operating anaccess node is provided. The method includes configuring, by the accessnode, preamble sequences on a BRACH resource to user equipments (UEs),receiving, by the access node, a beam failure recovery request messageincluding a sequence on a beam failure random access channel (BRACH)resource, identifying, by the access node, a UE associated with thesequence, and sending, by the access node, a beam failure recoveryresponse message including a transmission grant for the UE.

Optionally, in any of the preceding embodiments, an embodiment whereinthe method further comprises receiving, by the access node, recoveryinformation from the UE, setting up, by the access node, a controlchannel in accordance with the recovery information, and transmitting,by the access node, a control channel signal in accordance with a subsetof the recovery information.

Optionally, in any of the preceding embodiments, an embodiment whereinthe recovery information comprises a first identifier of a firstreference signal resource associated with a first reference signal typetransmitted by an access node, and wherein setting up the controlchannel comprises setting up the control channel in accordance with thefirst identifier.

Optionally, in any of the preceding embodiments, an embodiment whereinthe recovery information comprises a second identifier of a secondresource associated with a second reference signal transmitted by theaccess node and an intra-group identifier identifying a group of firstreference signal resources associated with a first reference signal typethat is spatially QCL with a second reference signal resource associatedwith a second reference signal type, and wherein setting up the controlchannel includes determining a first identifier of a first referencesignal resource associated with a first reference signal typetransmitted by an access node in accordance with the second identifierand the intra-group identifier, and setting up the control channel inaccordance with the first identifier.

Optionally, in any of the preceding embodiments, an embodiment whereinthe recovery information comprises an intra-group identifier identifyinga group of first reference signal resources associated with a firstreference signal type that is spatially QCL with a second referencesignal resource associated with a second reference signal type, andwherein setting up the control channel includes determining a secondidentifier of a second resource associated with the second referencesignal transmitted by the access node, determining a first identifier ofa first reference signal resource associated with a first referencesignal type transmitted by an access node in accordance with the secondidentifier and the intra-group identifier, and setting up the controlchannel in accordance with the first identifier.

Optionally, in any of the preceding embodiments, an embodiment whereinthe beam failure recovery response message comprises a transmissiongrant, and wherein the recovery information is received in accordancewith the transmission grant.

Optionally, in any of the preceding embodiments, an embodiment whereinthe method further comprises transmitting, by the access node, one ormore precoded first reference signals on one or more first referencesignal resources associated with a first reference signal type, andtransmitting, by the access node, one or more precoded second referencesignals on one or more second reference signal resources associated witha second reference signal type.

Optionally, in any of the preceding embodiments, an embodiment whereinthe method further comprises configuring, by the access node, thesequence for the UE.

Optionally, in any of the preceding embodiments, an embodiment whereinthe method further comprises sending, by the access node, an associationmessage conveying at least one of associations between one or morereference signal resources and one or more BRACH resources, associationsbetween the one or more BRACH resources and one or more BRACH responseresources, or associations between the one or more reference signalresources and the one or more BRACH response resources.

Optionally, in any of the preceding embodiments, an embodiment whereinthe method further comprises sending, by the access node, quasico-located (QCL) information between first reference signal resourcesassociated with a first reference signal type and second referencesignal resources associated with the second reference signal type.

In accordance with an example embodiment, a method for operating a userequipment (UE) is provided. The method includes determining, by the UE,a first identifier of a first reference signal resource associated witha first reference signal type transmitted by an access node,determining, by the UE, a second identifier of a second reference signalresource associated with a second reference signal type transmitted bythe access node, sending, by the UE, a beam failure recovery requestmessage including a sequence selected from one or more sequencesassociated with the UE, the beam failure recovery request message issent on a beam failure random access channel (BRACH) resource identifiedin accordance with the second identifier, and monitoring, by the UE, fora downlink control channel.

Optionally, in any of the preceding embodiments, an embodiment whereinthe method further comprises receiving, by the UE, a configuration ofthe plurality of sequences associated with the UE from the access node.

Optionally, in any of the preceding embodiments, an embodiment whereinthe method further comprises receiving, by the UE, an associationmessage conveying at least one of associations between one or morereference signal resources and one or more BRACH resources, associationsbetween the one or more reference signal resources and one or more BRACHresponse resources, or associations between the one or more BRACHresources and the one or more BRACH response resources.

Optionally, in any of the preceding embodiments, an embodiment whereinthe BRACH resource is further identified in accordance with theassociation message conveying associations between the one or morereference signal resources and the one or more BRACH resources.

Optionally, in any of the preceding embodiments, an embodiment whereinthe method further comprises receiving, by the UE, QCL informationbetween first reference signal resources associated with the firstreference signal type and second reference signal resources associatedwith the second reference signal type.

Optionally, in any of the preceding embodiments, an embodiment whereinthe second identifier of the second resource associated with the secondreference signal is determined in accordance with the QCL information.

Optionally, in any of the preceding embodiments, an embodiment whereinthe second identifier of the second resource associated with the secondreference signal is determined by monitoring second resources associatedwith the second reference signal.

Optionally, in any of the preceding embodiments, an embodiment whereinthe plurality of sequences associated with the UE comprises extendedsequences, wherein each extended sequence includes a base sequencecommon to all extended sequences and a unique tail sequence.

Optionally, in any of the preceding embodiments, an embodiment whereinthe plurality of sequences associated with the UE comprises sequencesthat are different from one another.

In accordance with an example embodiment, a method for operating anaccess node is provided. The method includes receiving, by the accessnode, a beam failure recovery request message including a sequence on abeam failure random access channel (BRACH) resource, identifying, by theaccess node, a user equipment (UE) associated with the sequence,determining, by the access node, a second identifier of a secondreference signal resource associated with a second reference signal typein accordance with a position of the BRACH resource, determining, by theaccess node, an intra-group identifier identifying a group of firstreference signal resources associated with a first reference signal typethat is spatially quasi co-located (QCL) with the second referencesignal resource associated with the second reference signal type,determining, by the access node, a first identifier of the firstreference signal resource associated with the first reference signaltype in accordance with the second identifier and the intra-groupidentifier, and setting up, by the access node, a control channel inaccordance with the first identifier.

Optionally, in any of the preceding embodiments, an embodiment whereinthe method further comprises configuring, by the access node, one ormore sequences for the UE, and sending, by the access node, theplurality of sequences to the UE.

Optionally, in any of the preceding embodiments, an embodiment whereinthe method further comprises transmitting, by the access node, precodedfirst reference signals on first reference signal resources associatedwith the first reference signal type, and transmitting, by the accessnode, precoded second reference signals on the second reference signalresources associated with the second reference signal type.

Optionally, in any of the preceding embodiments, an embodiment whereinthe method further comprises sending, by the access node, an associationmessage conveying at least one of associations between one or morereference signal resources and one or more BRACH resources, associationsbetween the one or more reference signal resources and one or more BRACHresponse resources, or associations between the one or more BRACHresources and the one or more BRACH response resources.

Optionally, in any of the preceding embodiments, an embodiment whereinthe method further comprises sending, by the access node, QCLinformation between first reference signal resources associated with afirst reference signal type and second reference signal resourcesassociated with the second reference signal type.

In accordance with an example embodiment, a method for operating a userequipment (UE) is provided. The method includes determining, by the UE,a beam index of a replacement beam in accordance with a first referencesignal received from an access node, identifying, by the UE, a beamfailure random access channel (BRACH) resource in accordance with thebeam index and an association between beam indices and block indices,and sending, by the UE, a preamble sequence in the BRACH resource.

Optionally, in any of the preceding embodiments, an embodiment whereinthe method further comprises receiving, by the UE, the associationbetween beam indices and block indices.

Optionally, in any of the preceding embodiments, an embodiment whereinthe association between beam indices and block indices is received fromthe access node.

Optionally, in any of the preceding embodiments, an embodiment whereinthe association between beam indices and block indices is a directassociation between the beam indices and the block indices.

Optionally, in any of the preceding embodiments, an embodiment whereinthe association between beam indices and block indices is an indirectassociation between the beam indices and the block indices.

Optionally, in any of the preceding embodiments, an embodiment whereinthe method further comprises selecting, by the UE, the preamble sequencefrom one or more preamble sequences.

In accordance with an example embodiment, a method for operating anaccess node is provided. The method includes receiving, by the accessnode from a user equipment (UE), a preamble sequence in a beam failurerandom access channel (BRACH) resource, determining, by the access node,a beam index of a replacement beam selected by the UE in accordance witha reference signal transmitted by the access node, wherein the beamindex is determined in accordance with a block index associated with theBRACH resource and an association between beam indices and blockindices, and completing, by the access node, a beam failure recoveryprocedure in accordance with the beam index.

Optionally, in any of the preceding embodiments, an embodiment whereinthe method further comprises signaling, by the access node, theassociation between beam indices and block indices.

Optionally, in any of the preceding embodiments, an embodiment whereinthe association between beam indices and block indices is signaled in aradio resource control (RRC) message.

Optionally, in any of the preceding embodiments, an embodiment whereinthe method further comprises identifying, by the access node, anidentity of the UE.

Optionally, in any of the preceding embodiments, an embodiment whereinthe beam failure recovery procedure is completed in accordance with theidentity of the UE.

In accordance with an example embodiment, a method for operating a userequipment (UE) is provided. The method includes selecting, by the UE, aresource for conveying a preamble to an access node from one or moreresources, wherein the plurality of resources is shared with other UEsin at least one of a code sequence domain, a time domain, or a frequencydomain, and sending, by the UE to the access node, a preamble associatedwith the UE in the selected resource.

In accordance with an example embodiment, a method for operating anaccess node is provided. The method includes configuring, by the accessnode, one or more resources for conveying preambles from user equipments(UEs), wherein the plurality of resources is shared by the UEs in atleast one of a code sequence domain, a time domain, or a frequencydomain, and sending, by the access node, the configuration to the UEs.

Optionally, in any of the preceding embodiments, an embodiment whereinthe method further comprises receiving, by the access node from a subsetof the UEs, preambles in the plurality of resources.

Practice of the foregoing embodiments enables UEs to participate andassist in beam recovery in the event of a beam loss or failure.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIG. 1 illustrates an example wireless communications system accordingto example embodiments described herein;

FIG. 2 illustrates an example beam tracking system according to exampleembodiments described herein;

FIG. 3A illustrates a flow diagram of example operations occurring in anaccess node participating in a beam recovery procedure according toexample embodiments described herein;

FIG. 3B illustrates a flow diagram of example operations occurring in aUE participating in a beam recovery procedure according to exampleembodiments described herein;

FIG. 4 illustrates a diagram highlighting an example one-to-oneassociation between transmit precoder of WBRS resources and receivecombiners of BRACH resources according to example embodiments describedherein;

FIG. 5 illustrates a diagram providing a detailed view of an exampleBRACH resource according to example embodiments described herein;

FIG. 6 illustrates a flow diagram of example operations occurring in anaccess node participating in beam recovery using a BFRS according toexample embodiments described herein;

FIG. 7 illustrates a diagram highlighting an example association betweenresources and beams used in beam recovery according to exampleembodiments described herein;

FIG. 8 illustrates a flow diagram of example operations occurring in aUE participating in beam recovery using a BFRS according to exampleembodiments described herein;

FIG. 9 illustrates a diagram highlighting UE communications in beamrecovery according to example embodiments described herein;

FIG. 10A illustrates a flow diagram of example operations occurring inan access node participating in beam recovery using a beam failure RSthat includes one or more reference signals according to exampleembodiments described herein;

FIG. 10B illustrates a flow diagram of example operations occurring in aUE participating in beam recovery where the UE monitors one or morereference signals according to example embodiments described herein;

FIG. 11 illustrates a diagram highlighting an example BRACH preambletransmission and response reception on multiple resources according toexample embodiments described herein;

FIG. 12 illustrates a diagram highlighting the sending of a BRACHpreamble and the detection of a response according to exampleembodiments described herein;

FIG. 13 illustrates a diagram of example beams for synchronizationsignals (SS) and CSI-RS according to example embodiments describedherein;

FIG. 14 illustrates a graphical representation of two precoders that arespatially quasi-co-located (QCLed) according to example embodimentsdescribed herein;

FIG. 15 illustrates a diagram of beam patterns of precoders for a firstbeam and one or more second beams, where the precoders have aone-to-many SQCL (OMSQ) relationship according to example embodimentsdescribed herein;

FIG. 16 illustrates a diagram of beam patterns of precoded signals,highlighting potential relationships according to example embodimentsdescribed herein;

FIG. 17 illustrates a flow diagram of operations occurring in an accessnode utilizing OMSQ relationships to change beams according to exampleembodiments described herein;

FIG. 18 illustrates a flow diagram of operations occurring in a UEutilizing OMSQ relationships to change beams according to exampleembodiments described herein;

FIG. 19 illustrates first example BRACH resources according to exampleembodiments described herein;

FIGS. 20A and 20B illustrate tables of relative indices of block indicesof an example BRACH block configuration and relative indices of beamindices of CSI-RS according to example embodiments described herein;

FIG. 20C illustrates a table of an example direct association betweenbeam indices and block indices according to example embodimentsdescribed herein;

FIG. 21 illustrates second example BRACH resources according to exampleembodiments described herein;

FIG. 22A illustrates a flow diagram of example operations occurring in aUE initiating beam failure recovery according to example embodimentsdescribed herein;

FIG. 22B illustrates a flow diagram of example operations occurring inan access node participating in beam failure recovery according toexample embodiments described herein;

FIG. 23 illustrates an example communication system according to exampleembodiments described herein;

FIGS. 24A and 24B illustrate example devices that may implement themethods and teachings according to this disclosure; and

FIG. 25 is a block diagram of a computing system that may be used forimplementing the devices and methods disclosed herein.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of the example embodiments are discussed in detailbelow. It should be appreciated, however, that the present disclosureprovides many applicable inventive concepts that can be embodied in awide variety of specific contexts. The specific embodiments discussedare merely illustrative of specific ways to make and use theembodiments, and do not limit the scope of the disclosure.

FIG. 1 illustrates an example wireless communications system 100.Communications system 100 includes an access node 105 serving a userequipment (UE) 115. In a first operating mode, communications to andfrom UE 115 pass through access node 105. In a second operating mode,communications to and from UE 115 do not pass through access node 105,however, access node 105 typically allocates resources used by UE 115 tocommunicate. Access nodes may also be commonly referred to as evolvedNodeBs (eNBs), base stations, NodeBs, master eNBs (MeNBs), secondaryeNBs (SeNBs), next generation (NG) NodeBs (gNBs), master gNBs (MgNBs),secondary gNBs (SgNBs), remote radio heads, access points, and the like,while UEs may also be commonly referred to as mobiles, mobile stations,terminals, subscribers, users, stations, and the like.

While it is understood that communications systems may employ multipleaccess nodes capable of communicating with a number of UEs, only oneaccess node and one UE are illustrated for simplicity.

As discussed previously, pathloss in communications systems operating athigh frequency (HF) (6 gigahertz (GHz) and above, such as millimeterwavelength (mmWave)) operating frequencies is high, and beamforming maybe used to overcome the high pathloss. As shown in FIG. 1, both accessnode 105 and UE 115 communicate using beamformed transmissions andreceptions. As an example access node 105 communicates using one or morecommunications beams, including beams 110 and 112, while UE 115communicates using one or more communications beams, including beams 120and 122.

A beam may be a pre-defined set of beamforming weights in the context ofcodebook-based precoding or a dynamically defined set of beamformingweights in the context of non-codebook based precoding (e.g.,Eigen-based beamforming (EBB)). A beam may also be a pre-defined set ofphase shift preprocessors combining signals from the antenna array inthe radio frequency (RF) domain. It should be appreciated that a UE mayrely on codebook-based precoding to transmit uplink signals and receivedownlink signals, while a TRP may rely on non-codebook based precodingto form certain radiation patterns to transmit downlink signals and/orreceive uplink signals.

A variety of limitations exist that may limit the performance of a UE,the limitations include:

-   -   Electromagnetic coupling: The electric currents on the surface        of the antenna of the UE induce various forms of electric        magnetic coupling, which affects the characteristic impedance        and antenna aperture efficiency;    -   Physical size: In general, the display panel and battery of a UE        occupy the largest percentage of the volume of the UE, while        various other devices (including sensors, cameras, speakers,        etc.) also take up a significant portion of the remaining volume        and are usually placed on the edges of the UE. Antennas (third        generation (3G), fourth generation (4G), fifth generation (5G)        new radio (NR), and so on) are also present. Power consumption,        heat dissipation, and so forth, also have an impact on physical        size;    -   Usage: The intended usage of the UE also has an impact on the        performance of UE; As an example, the hand of the use may reduce        the gain of the antenna array by an average of 10 dB when it        completely encompasses the array; and    -   Antenna array configuration: Multiple antenna arrays may be        used; potentially requiring multiple radio frequency (RF)        integrated circuits (ICs) and a single baseband (BB) IC (BBIC).

It is noted that the movement of the UE may lead to significantdegradation in the signal quality. However, the movement may be detectedusing a variety of sensors, including:

-   -   Three dimensional (3D) gyroscopes with a root mean squared (RMS)        noise on the order of 0.04 degrees per second;    -   3D accelerometers with a RMS noise on the order of 1 milli-g;        and    -   Magnetometers.        If the movement of the UE is known, it may possible to quickly        track the beams used by the UE.

FIG. 2 illustrates an example beam tracking system 200. Beam trackingsystem 200 may be located in a UE. Beam tracking system 200 uses datafrom one or more sensors (including position information frominformation assisted positioning systems (such as a Global PositioningSystem (GPS)), 3G gyroscopic information, 3D accelerometer information,magnetometer information, and so on) to perform beam tracking. A dataunit 205 receives sensor data and processes the data, providing theprocessed data to a movement classification unit 210 that classifies thetype of movement the UE is undergoing. Movement classification unit 210also receives information from a training data unit 215 that providesinformation to movement classification unit 210 based on historical datato help in the classification of the movement of the UE. The classifiedmovement is provided to a detector 220. Detector 220 may consider if themovement of the UE warrants beam tracking adjustments. Should beamtracking adjustments be warranted, beam tracking adjustment solutionsare generated. Examples of solutions include a beam adjustment for asituation where the UE is standing still 225, a beam adjustment for asituation where the UE is rotating 226, a beam adjustment for asituation where the UE is experiencing a displacement 227, and a beamadjustment for a situation where the UE is blocked 228.

Resources may be allocated for beam recovery purposes. As used herein,the resources refer to time resources, frequency resources, preamblesequence resources, or a combination thereof. The beam recoveryresources may be allocated when a UE establishes an active link with theaccess node. Each UE may be assigned one or more unique beam recoveryresources. In a first example embodiment, the beam recovery resourcesare beam recovery random access channel (BRACH) preambles, which may betransmitted in a BRACH region. It is noted that the BRACH region may bethe same or different from a physical random access channel (PRACH)region used for initial access purposes in terms of time and/orfrequency locations within the entire operating band. In a secondexample embodiment, the beam recovery resources are sets of uniqueresources (i.e., each UE may be allocated multiple resources), where foreach UE, each resource can be used for beam recovery purposes. As usedherein, resources, regions and preambles for beam failure recovery arereferred to BRACH resources, regions, and preambles. It is noted thatthey may also be referred to as PRACH resources, regions, and preamblesfor beam failure recovery purpose as well. The discussion presented herewill use BRACH for simplicity.

With regard to the BRACH and PRACH, in a first example embodiment, ifthe two channels use different or orthogonal resources in time orfrequency, the same sequence may be used in both the BRACH and thePRACH. As an illustrative example, if a UE is assigned a first sequenceto transmit in the PRACH region, the UE may also use the first sequenceto transmit in the BRACH region. In a second example embodiment, if thesame sequence is used as the PRACH preamble and the BRACH preamble,different scrambling codes may be used. As an illustrative example, if afirst UE is assigned to use the first sequence to transmit in the PRACHregion, the first sequence, when scrambled by a first scramblingsequence, may be used by the first UE to transmit in the BRACH region.It is noted that the scrambling sequence for different UEs may be thesame or different. It is also noted that multiple BRACH resources mayexist, each occupying a different time-frequency location. In such asituation, the same sequence may be used in different BRACHs.

In a third example embodiment, the sequences used as the PRACH preamblesequence and the BRACH preamble sequence itself may be orthogonal. In afourth example embodiment, if the BRACH and PRACH channels use the sameand/or overlapping time and/or frequency resources, the PRACH preamblesequence and the BRACH preamble sequence may be orthogonal to eachother. It is noted that multiple BRACH resources may exist, eachoccupying the same time and/or frequency position. In such a situation,multiple orthogonal preamble sequences may be used for multiple BRACHresources, each uniquely identifying a unique BRACH resource. Overall,for each UE, multiple BRACH channels may exist and each BRACH channelmay be uniquely identified by the time and/or frequency location as wellas the preamble sequence used by the UE to convey the beam failureevent.

FIG. 3A illustrates a flow diagram of example operations 300 occurringin an access node participating in a beam recovery procedure. Operations300 may be indicative of operations occurring in an access node as theaccess node participates in a beam recovery procedure.

Operations 300 begin with the access node configuring BRACH preamblesequences (block 305). In general the configuration may be transmittedto a UE in a radio resource configuration message, medium access controlelement message, downlink control indicator message, or a combinationthereof. The configuration message should provide to the UE informationregarding which preamble sequence to use, at which time position andfrequency position to transmit the preamble, e.g., the time andfrequency location of the BRACH channel, and so forth. The BRACHpreamble sequences may be transmitted by the UE over the BRACH channelswhen needed, such as to request beam recovery. The access node mayconfigure a unique BRACH preamble sequence for each UE. Alternatively, asingle BRACH preamble sequence may be assigned to multiple UEs.Alternatively, multiple BRACH preamble sequences may be assigned to eachUE. The access node also conveys the BRACH preamble sequences to theUEs. The access node sends, e.g., broadcasts, reference signals toassist the UEs in detecting beam failure as well as new beamidentification (block 307). The reference signals may include beamrecovery reference signals (BRRS), wide beam reference signals (WBRS)(such as synchronization signals (SS), wide beam channel stateinformation reference signals (WB CSI-RS), broad-beam CSI-RS,SS-mimicking CSI-RS, cell-specific CSI-RS, group CSI-RS, common CSI-RS,Layer 3 mobility CSI-RS, and so on), channel state information referencesignals (CSI-RS), and so on, may be transmitted by the access node sothat a UE may measure to determine if a beam failure has occurred. Thereference signals may also help the UE determine recovery informationuseful in the setting up of a replacement DL control channel, or inother words, if a new beam has been identified. In the subsequentdiscussion, the term beam failure reference signal (BFRS) is used torepresent the above reference signals, which may include BRRSs, WBRSs,CSI-RSs, or combinations thereof. It is noted that the reference signalfor beam failure determination or detection and the reference signal fornew beam identification may be the same set of reference signals, ordifferent sets of reference signals. The access node receives a BRACHpreamble from a UE at a BRACH channel (block 309). The access nodetransmits a Beam Recovery Request Response (block 310), which may, ormay not, include an UL grant for the UE to transmit further recoveryinformation. If the UL grant for the UE to transmit further recoveryinformation is included, the access node receives extra recoveryinformation from the UE (block 311). The extra recovery information mayinclude information useful in setting up a DL control channel with theUE. The access node sets up a DL control channel (block 313). The accessnode sends DL control messages on the DL control channel (block 315).The DL control messages may include control signaling. In an alternativeembodiment, blocks 309 and 311 may be performed together, meaning thatthe preamble as well as the recovery information is received by theaccess node in a single transmission. In such a situation, blocks 310,313, and 315 may be performed together.

FIG. 3B illustrates a flow diagram of example operations 350 occurringin a UE participating in a beam recovery procedure. Operations 350 maybe indicative of operations occurring in a UE as the UE participates ina beam recovery procedure.

Operations 350 begin with the UE receiving a BRACH preamble sequenceconfiguration as well as BRACH channel configuration from an access node(block 355). As discussed previously, the BRACH preamble sequenceconfiguration provides information to the UE regarding which preamble totransmit in case of beam failure, while the BRACH channel configurationprovides information to the UE regarding at which time and frequencyposition to transmit the BRACH preamble sequence. Such configurationmessages may be received by the UE in a radio resource control (RRC)message, medium access control (MAC) control element (CE) (MAC-CE)message, downlink control indicator (DCI) message, or a combinationthereof. The UE monitors downlink (DL) channels or signals, e.g., DLcontrol channels, DL reference signals, synchronization signals, and soon (block 357). The UE may monitor the DL channels or signals todetermine if a beam failure or loss has occurred. As an example, if theUE is unable to detect the existence of a particular resource, such asBRRS, WBRS (such as SS, WB CSI-RS, broad-beam CSI-RS, SS-mimickingCSI-RS, cell-specific CSI-RS, group CSI-RS, common CSI-RS, and so on),CSI-RS (such as narrow beam CSI-RS, UE-specific CSI-RS, Layer 3 mobilityCSI-RS, and so forth), etc., the UE may determine that a beam failurehas occurred. The UE performs a check to determine if beam failure hasoccurred (block 359). If a beam failure has not occurred, the UE returnsto block 357 to continue to monitor the DL channels or signals. As anexample, if the measurement made by the UE does not meet a beam failurecondition, the UE determines that a beam failure has not occurred. Ifthe measurement does meet the beam failure condition, the UE determinesthat a beam failure has occurred.

If a beam failure has occurred, the UE performs measurements of BFRSsand obtains recovery information (block 361). As an illustrativeexample, the UE measures certain reference signals, i.e., BFRS, such asBRSS, WBRS, CSI-RS, etc., to re-detect or re-synchronize with beamstransmitted by the access node. The UE may determine recoveryinformation, including DL transmit beam(s) (or associated index/indices)of the reference signals from the access node or which DL transmit beamprovides sufficient quality. In other words, the UE determines with DLtransmit beam has a signal quality that meets a threshold, which may bespecified in a technical standard, an operator of the communicationssystem, or determined through collaboration between the UE and theaccess node. Alternatively, the UE selects the DL transmit beam with thehighest signal quality. The measurements may also improve time orfrequency synchronization. The location in time or frequency of thereference signals may be signaled from the access node a priori and maybe periodically allocated in the time and frequency domains. Such asignaling may be included in a RRC message, a MAC-CE message, a DCImessage, or a combination thereof.

The UE transmits the BRACH preamble (block 363) if a beam failure hasbeen detected and a new beam been identified. The transmission of theBRACH preamble initiates beam recovery. In a first example embodiment,the UE transmits its own preamble sequence in the BRACH region. TheBRACH region may be non-orthogonal or orthogonal to the PRACH region inthe time or frequency domain. In a second example embodiment, the UEtransmits control or commands in a grant-free manner on resourceelements (REs). The transmission of control or commands is a grant-freeapproach and may use REs pre-allocated to the UE. The uplink (UL)transmission may rely on time or frequency synchronization performedpreviously. The UE monitor DL channels for Beam Recovery RequestResponse that may, or may not, include an UL grant to transmit extrarecovery information (block 364). If a UL grant is received, the UEtransmits extra recovery information (block 365). The extra recoveryinformation may include an index or indices of DL transmit beams or DLreference signals for new beam identification from the access node,channel quality indication(s) (such as reference signal received power(RSRP), reference signal received quality (RSRQ), received signalstrength, signal to noise ratio (SNR), signal to noise plus interferenceratio (SINR), received signal strength indicator (RSSI), and so on), aswell as other information useful to the access node in the setting up ofa DL control channel. The UE receives DL control messages on a DLcontrol channel setup by the access node (block 367). Alternatively,blocks 363 and 365 may occur in a single transmission. In thissituation, block 364 and block 367 may occur together.

In general, a UE may monitor a reference signal, such as a BFRS todetermine if a beam failure condition has been met and if a new beam hasbeen identified. As an example, a BFRS includes a set of CSI-RSs forbeam management purposes. As another example, BFRS includes a set ofSSs. In general, BFRS includes CSI-RSs, WBRSs, or both CSI-RSs andWBRSs. It is noted that the reference signals for beam failuredetermination or detection and the reference signals for new beamidentification may be the same set of reference signals, or differentset of reference signals. In other words, the reference signal for beamfailure detection includes CSI-RSs, WBRSs, or both CSI-RSs and WBRSs,and the reference signal for new beam identification includes CSI-RSs,WBRSs, or both CSI-RSs and WBRSs.

According to an example embodiment, techniques utilizing a BFRS (forbeam failure detection and new beam identification) that includes both aset of CSI-RSs and a set of WBRS are provided. It is noted that the BFRSincluding the reference signal for beam failure detection with bothCSI-RS and WBRS, and the new reference signal for beam identificationalso with both CSI-RS and WBRS is one example embodiment. Other exampleembodiments include: the reference signal for beam failure detectionincludes CSI-RS only, WBRS-only, or both; and the new reference signalfor beam failure identification includes CSI-RS only, WBRS-only, orboth. According to another example embodiment, techniques utilizing abeam failure RS that includes only a CSI-RS are provided. Both exampleembodiments use a common framework. A difference in the exampleembodiment exists in which a UE uses a single BRACH resource (identifiedusing detected CSI-RS, WBRS, or a combination thereof) or multiple BRACHresources to transmit the BRACH preamble.

An example communications system as presented below is used tofacilitate discussion. However, the example embodiments presented hereinare operable with other communications system configurations. Theexample communications system includes:

-   -   Access nodes that configure the UEs with one or more unique        BRACH preamble sequences within a BRACH region. A UE, for beam        recovery purposes, may use one of the configured BRACH preamble        sequence to send a beam recovery request on the BRACH region.        Usually, the BRACH region is parameterized by at least its time        and frequency location information, and the time-frequency        parameters may be included in a radio resource configuration        message.    -   Access nodes send out multiple BFRSs (including WBRSs or CSI-RSs        or both) in N resources (where N is an integer number). A        different precoding of the BFRS may be used in different        resources. It is noted that herein the BFRS is used mainly for        the function of new beam identification, but it is possible to        use the BFRS for the function of beam failure detection.    -   Access nodes may configure B BRACH regions or resources (where B        is an integer number), e.g., via a RRC message, MAC-CE message,        DCI message, or a combination thereof. As an example, B=N, but        it is not necessary that B=N. The N BRACH regions or resources        may occur after the N BFRS resources (i.e., the resources        containing the N BFRSs). The access nodes may signal a        relationship or association between the N (as well as B in        general) BRACH resources and the N BFRS resources. To        generalize, the access node may signal a relationship or        association between the N BRACH resources and the N BFRS        resources. An illustrative example of the relationship or        association is that the transmit precoder of the N BFRS        resources and the receive combiner (also commonly referred to as        a precoder at the receiver side) of the N BRACH resources have a        one-to-one association, e.g., a transmit precoder of a first        BFRS resource has a reciprocal beam correspondence relationship        with a receive combiner of a first BRACH resource. Another        illustrative example of the relationship or association is that        the locations of the N BRACH resources in time-frequency can be        determined from the locations of the N BFRS resources in        time-frequency relative to a reference resource, or vice versa.        In other words, if a first BFRS resource containing a first BFRS        reference signal is identified, a first BRACH resource in a        first time-frequency location should be used by the UE to        transmit the beam failure recovery preamble sequence; and so on        and so forth. Conversely, if a first BRACH resource in a first        time-frequency location is used by the UE to transmit the beam        failure recovery preamble sequence, it should explicitly or        implicitly inform the access node that a first BFRS resource        containing a first BFRS reference signal has been identified by        the UE; and so on and so forth. Alternatively, the relationship        is specified in a technical standard or by an operator of the        communications system. If the relationship or association is        specified in a technical standard or by an operator of the        communications system, explicit signaling of such a relationship        or association may not be needed.

FIG. 4 illustrates a diagram 400 highlighting an example one-to-oneassociation between transmit precoder of WBRS resources and receivecombiners of BRACH resources. As shown in FIG. 4, a BFRS region 405presents BFRS resources 407, 408, and 409, as well as DL transmit beams410, 411, and 412, of an access node, while a BRACH region 415 presentsBRACH resources 417, 418, and 419, as well as UL receive beams 420, 421,and 422 of the access node. It is noted that although communicationsbeam of the access node are displayed in FIG. 4, similar beams of a UEmay be shown in their place.

As shown in diagram 400, there is a one-to-one association or relationbetween the transmit precoders of the DL transmit beams of the accessnode and the receive combiners of the UL receive beams of the accessnode. In the particular example illustrated in FIG. 4, the one-to-oneassociation or relation is referred to as beam correspondence (BC). Incommunications systems that are operating at higher frequencies, such asmillimeter wavelength (mmWave) communications systems, communicationsdevices generally have a large number of transmit or receive antennasthat share a smaller number of radio frequency (RF) chains. From theperspective of a communications device, the beamformed transmit andreceive beams should have the same (or substantially the same) beampattern (in terms of peak or non-peak beam direction, peak or non-peakbeam gain, peak or non-peak beam width, and so on, for example) in thespatial domain. This means that for each beamformed beam, the beamresponse on all directions should be the same (or substantially thesame) from the point of view of the transmitter and the receiver. Thisis known as the beam correspondence condition, and when the beamcorrespondence condition is met, beam correspondence is achieved. Forexample, the transmit precoder of DL transmit beam 410 and the receivecombiner of UL receive beam 420 have beam correspondence. Alsoillustrated in FIG. 4 is an association or relation of thetime-frequency location of the BRACH resource and the BFRS resources.For example, if a BFRS at position 407 is identified as a recovered newbeam, then BRACH resource 417 (at a certain time-frequency location)should be used by the UE to transmit the beam failure recovery preamblesequence; conversely, if a BRACH resource 417 (at a certaintime-frequency location) is used by the UE to transmit the beam failurerecovery preamble sequence, it should convey that a BFRS at position 407has been identified as a recovered new beam.

FIG. 5 illustrates a diagram 500 providing a detailed view of an exampleBRACH resource. As shown in FIG. 5, a BRACH region 505 presents BRACHresources, such as BRACH resource 507. A BRACH resource, such as BRACHresource 507, may include time and frequency locations. As shown indiagram 500, BRACH resource 507 includes one or more time locations andone or more frequency locations. BRACH resource 507 includes firstresource 510 allocated for PRACH transmissions and second resource 512allocated for BRACH transmissions. In the above illustration, each BRACHresource, such as BRACH resource 507, includes BRACH resources (such assecond resource 512), and a UE may choose one BRACH resource out of NBRACH resources, with block index n, to send a pre-allocated preamble.The block index n can convey a piece of information of log 2(N)-bitsfrom the UE to the access node. This piece of information may be used toconvey from UE to access node which BFRS (out of the N BFRSs) has beenidentified by the UE. Typically, the access node may send a message(e.g., RRC message, MAC-CE message, DCI message, or a combinationthereof) in advance to the UE to configure the association between BRACHblocks and information conveyed therein, so that both access node and UEknow that sending the preamble on a first of N BRACH resourcesrepresents “00 . . . 01” meaning that a first of N BFRSs has beenidentified, sending the preamble on a second of N BRACH resourcesrepresents “00 . . . 10” meaning that a second of N BFRSs has beenidentified, . . . , and sending the preamble on an N-th of N BRACHresources represents “11 . . . 11” meaning that a Nth of N BFRSs hasbeen identified, and so on and so forth, while each bit sequence here islog 2(N)-bit long, and can represent the new identified beam index ofthe N BFRSs from the UE, for example. Alternatively, for each of the NBRACH resources, the BRACH resource within may be duplicated K timesleading to overall K*N BRACH resources, and the UE may choose one out ofK*N BRACH resources to send the pre-allocated preamble, while the blockindex n can convey log 2(K*N) bits of information from the UE to theaccess node. Typically, the access node may send a message in advance tothe UE, so that both access node and UE are aware of the associationbetween BRACH blocks and information conveyed therein. As an example,the information conveyed by the BRACH block index represents a newidentified beam index from the UE. The BRACH blocks may also includeresources for other uses. In some example embodiments, a BRACH resourcemay be allocated solely for BRACH transmissions. It is noted that thechannels of BRACH and PRACH may be different in terms of time and/orfrequency locations.

According to an example embodiment, techniques for beam failure recoveryutilizing a BFRS that includes two different sets of BFRSs, e.g., a setof first BFRSs and a set of second BFRSs, are provided. It is noted thatthe two sets of BFRSs may be two sub-sets of the available BFRSs. It isalso possible that in certain case only one set of reference signals isneeded, e.g., only the set of first BFRSs or only the set of secondBFRSs, which can be thought of as the special case of the approach thatuses the two sets of BFRSs. The inclusion of two different sets of BFRSsenables a UE to identify more choices of beams from an access node thatare candidates for replacing the failed beam, possibly using amultilayered approach that potentially simplifies detection anddecoding, as well as reduces signaling overhead. As an illustrativeexample, rather than scanning for a large number of narrow beamwidthbeams (e.g., the CSI-RS), which may require considerable time, the UEcan scan for a smaller number of wide beamwidth beams (e.g., the WBRS).Scanning for the smaller number of wide beamwidth beams reduces thescanning time required, thereby resulting in the search space for therecovered beam being significantly smaller than the search space for thenarrow beamwidth beams. Once the wide beamwidth beam(s) has beenidentified, the UE can scan for a much smaller number of narrowbeamwidth beams that may be candidate beams for replacing the failedbeam.

FIG. 6 illustrates a flow diagram of example operations 600 occurring inan access node participating in beam recovery using a BFRS. Operations600 may be indicative of operations occurring in an access node as theaccess node participates in beam recovery using a BFRS. The BFRS mayinclude two different reference signals, e.g., a CSI-RS and a WBRS. TheBFRS may, alternatively, include one reference signal, e.g., CSI-RS orWBRS only.

Operations 600 begin with the access node configuring BRACH preamblesequences (block 605). The access node may configure a unique BRACHpreamble sequence for each UE. Alternatively, a single BRACH preamblesequence may be assigned to multiple UEs. Alternatively, multiple BRACHpreamble sequences may be assigned to each UE. The access node alsosends information regarding the BRACH preamble sequences to the UEs,e.g., via a RRC message, a MAC-CE message, a DCI message, or acombination thereof. The access node optionally sends relationships orassociations between BFRSs and BRACH resources, as well as BRACHresponse resources, to the UEs (block 607). The relationships orassociations between the BFRS resources and the BRACH resources (as wellas the BRACH response resources) may be fixed and can assist the UE indetermining which BRACH resource, at least in terms of time-frequencylocation, to use to transmit a BRACH preamble. In other words, a UEneeds to know the time-frequency location of a first BRACH resource totransmit the preamble sequence if a first BFRS is identified as the newbeam by the UE, the time-frequency location of a second BRACH resourceto transmit the preamble sequence if a second BFRS is identified as thenew beam; and so on and so forth. Conversely, an access node needs toknow that a first BFRS has been identified as the new beam by the UE ifit receives a preamble sequence at the time-frequency location of afirst BRACH resource; that a second BFRS has been identified as the newbeam by the UE if it receives a preamble sequence at the time-frequencylocation of a second BRACH resource; and so on and so forth. Theassociation or relation can also assist the UE in determining whichBRACH response resource to receive a response to the BRACH preamble. Adetailed discussion of the associations between the BFRSs and BRACHresources is provided below.

The relationships or associations between BFRSs and BRACH resources, aswell as BRACH response resources may be presented in data form to enablesimple and efficient signaling. As an illustrative example, consider asituation where the BFRS resources are denoted: 1a, 1b, 1c, and so on;the BRACH resources are denoted: 2a, 2b, 2c, and so on; and the BRACHresponse resources are denoted: a, b, c, and so on. In a firstillustrative example, the relationships or associations may be signaledpairs, such as:

1a, 2a to convey that resources 1a and 2a are associated or have arelationship;

1b, 2b to convey that resources 1b and 2b are associated or have arelationship;

1c, 2c to convey that resources 1c and 2c are associated or have arelationship;

1c, 2b to convey that resources 1c and 2b are associated or have arelationship

1a, a to convey that resources 1a and a are associated or have arelationship;

1b, b to convey that resources 1b and b are associated or have arelationship; and

1b, c to convey that resources 1b and c are associated or have arelationship.

The example relationships or associations may also be signaled intabular form listing associated resources, such as:

1a, 2a to convey that resources 1a and 2a are associated or have arelationship;

1b, 2b to convey that resources 1b and 2b are associated or have arelationship;

1c, 2b, 2c to convey that resources 1c and 2b and 2c are associated orhave a relationship;

1a, a to convey that resources 1a and a are associated or have arelationship; and

1b, b, c to convey that resources 1b and b and c are associated or havea relationship.

The access node sends the BFRS, including WBRSs only, CSI-RSs only, orboth WBRSs and CSI-RS, for example, using DL transmit beams (block 609).In the situation where the BFRS includes only CSI-RSs or WBRSs, theaccess node would only send CSI-RSs or WBRSs on DL transmit beams, forexample. However, if the BFRS includes both CSI-RSs and WBRSs, theaccess node would send both CSI-RSs and WBRSs on DL transmit beams. Theaccess node receives a BRACH preamble from a UE that has experienced abeam failure (block 611). As an illustrative example, when the BFRSincludes both CSI-RSs and WBRSs, the BRACH preamble is received on aBRACH resource associated with an m-th BFRS. In other words, the BRACHpreamble is received on the BRACH resource that was associated with them-th BFRS. As another illustrative example, when the BFRS includes onlyCSI-RSs or WBRSs, the BRACH preamble is received on a BRACH resourceassociated with an n-th BFRS. Furthermore, the BRACH preamble isreceived on an UL receive beam of the access node that is beamcorrespondent to a DL transmit beam of the access node used to transmitthe m-th or n-th BFRS. The access node identifies the UE (block 613).The access node may be able to identify the UE in accordance with theBRACH preamble, for example. The access node may also be able toidentify the new beam of the UE in accordance with the BRACH time andfrequency location. As an example, the access node may use thetechniques presented in FIG. 4 and associated discussion, wherein forexample, if a BRACH resource 417 (at a certain time-frequency location)is used by the UE to transmit the beam failure recovery preamblesequence, the use of BRACH resource 417 conveys information that a BFRSat position 407 has been identified as a recovered new beam. The accessnode may, or may not generate an UL resource grant for the UE (block615). The UL resource grant is for allocating resources to allow the UEto transmit extra recovery information to the access node. The accessnode sends a response, e.g., a BFR response, with, optionally, the ULresource grant (or information related thereto) to the UE (block 617).In the situation where the beam failure RACH response includes the ULresource grant (or information related thereto), the access nodereceives an UL transmission (block 619), which includes the extrarecovery information from the UE. The extra recovery information mayinclude additional information related to n, for example. The accessnode rebuilds a DL control channel or assists in beam management (block621). The access node utilizes the extra recovery information providedby the UE to rebuild the DL control channel or assist in beammanagement. It is noted that blocks 611 and 619 may occur at the sametime, and blocks 613, 615, 617, and 621 may occur at the same time,afterwards. It is further noted that blocks 611 and 619 may be mergedinto a single block in the case where the BFRS comprises only CSI-RSs orWBRSs.

FIG. 7 illustrates a diagram 700 highlighting an example associationbetween resources and beams used in beam recovery. As shown in FIG. 7, aBFRS region 705 presents BFRS resources (e.g., BFRS resource 710) andaccess node DL transmit beams (e.g., beam 715) used to transmit BFRS, aBRACH region 707 presents BRACH resources (e.g., BRACH resource 712) andUL receive beams (e.g., beam 717) used to receive BRACH preambles and ULtransmit beams (e.g., beam 722) used to transmit BRACH preambles, and aresponse region 709 presents response resources (e.g., response resource714) and UL receive beams (e.g., beam 719) used to receive responses. Itis noted that a precoder of beam 715 and a combiner of beam 717 may bebeam correspondent, and a precoder of beam 722 and a combiner of beam719 may be beam correspondent. Furthermore, there is a one-to-oneassociation between BFRS resource 710 and BRACH resource 712, as well asa one-to-one association between BRACH resource 712 and responseresource 714.

The beam correspondence between various beams and the one-to-oneassociations between the resources help the access node and the UEdetermine which resources and beams to use to receive and transmit. Asan example, if the UE has determined that a BFRS transmitted by DLtransmit beam 715 is its selected best candidate among the multiplecandidate BFRSs, the UE is able to determine (from beam correspondenceand the one-to-one associations, for example) that it should transmit aBRACH preamble in BRACH resource 712 while using beam 722. Furthermore,the UE is able to determine (again, from beam correspondence and theone-to-one associations) that it should monitor or receive a response inresponse resource 714, possibly using beam 719. Clearly, the use of beamcorrespondence and the one-to-one associations simplify thedetermination of which resources and beams to use.

FIG. 8 illustrates a flow diagram of example operations 800 occurring ina UE participating in beam recovery using a BFRS. Operations 800 may beindicative of operations occurring in a UE as the UE participates inbeam recovery using a BFRS. The BFRS may include two different referencesignals, e.g., a CSI-RS and a WBRS. The BFRS may, alternatively, includeone reference signal, e.g., CSI-RS or WBRS only.

Operations 800 begin with the UE receiving a BRACH preamble sequenceconfiguration from an access node (block 805). The UE optionallyreceives relationships or associations between BFRS resources and BRACHresources, as well as BRACH response resources from the access node(block 807). The relationships or associations between the BFRSresources and the BRACH resources (as well as the BRACH responseresources) may be fixed and can assist the UE in determining which BRACHresource to use to transmit a BRACH preamble, and potentially, whichBRACH response resource to receive a response to the BRACH preamble.

The relationships or associations between BFRSs and BRACH resources, aswell as BRACH response resources may be presented in data form to enablesimple and efficient signaling. As an illustrative example, consider asituation where the BFRS resources are denoted: 1a, 1b, 1c, and so on;the BRACH resources are denoted: 2a, 2b, 2c, and so on; and the BRACHresponse resources are denoted: a, b, c, and so on. In a firstillustrative example, the relationships or associations may be signaledpairs, such as:

1a, 2a to convey that resources 1a and 2a are associated or have arelationship;

1b, 2b to convey that resources 1b and 2b are associated or have arelationship;

1c, 2c to convey that resources 1c and 2c are associated or have arelationship;

1c, 2b to convey that resources 1c and 2b are associated or have arelationship

1a, a to convey that resources 1a and a are associated or have arelationship;

1b, b to convey that resources 1b and b are associated or have arelationship; and

1b, c to convey that resources 1b and c are associated or have arelationship.

The example relationships or associations may also be signaled intabular form listing associated resources, such as:

1a, 2a to convey that resources 1a and 2a are associated or have arelationship;

1b, 2b to convey that resources 1b and 2b are associated or have arelationship;

1c, 2b, 2c to convey that resources 1c and 2b and 2c are associated orhave a relationship;

1a, a to convey that resources 1a and a are associated or have arelationship; and

1b, b, c to convey that resources 1b and b and c are associated or havea relationship.

The UE monitors the BFRS (e.g., CSI-RSs, WBRSs, or both CSI-RSs andWBRSs and determines index (indices) of best BFRS (e.g., CSI-RS beam(s),WBRS beam(s), or CSI-RS and WBRS beams) (block 809). As a result ofmonitoring, the UE obtains a beam index per CSI-RS only, per WBRS only,or per CSI-RS and WBRS beams. The beam index may be represented byresource index n (an integer value). In a situation where the BFRSincludes only either CSI-RS or WBRS, the beam index is either the beamindex of the CSI-RS or the WBRS (the reference signal present in theBFRS). While, in a situation where the BFRS includes both CSI-RS andWBRS, the beam index may be either be the beam index of the CSI-RS orthe WBRS, depending on which beam (CSI-RS or WBRS) is better. Becausethe beam index may be the beam index of the CSI-RS or the WBRS, a reportof the beam index should make it clear which reference signal the beamindex is associated with. As an illustrative example, consider asituation where there are four CSI-RS beams and four WBRS beams. Then,beam indices 1 to 4 may be used for the four CSI-RS beams and beamindices 5 to 8 may be used for the four WBRS beams, for instance. Then,there would be no confusion as to which reference signal the beam indexis associated with. It is noted that the UE may obtain more than onebeam index. In such a situation, the indices are denoted n1, n2, and soon. As an example, in the situation where BFRS comprises CSI-RS, then-th CSI-RS resource out of the N possible CSI-RS resources may be thebest (in terms of quality, for example) from the point of view of the UEand may be used by the access node to rebuild a DL control channel or toassist in beam management.

The UE may determine remaining index (or indices) of the best BFRSbeam(s) (block 811), which may include CSI-RSs only, or WBRSs only. In asituation where the BFRS includes both CSI-RSs and WBRSs, the UE waspreviously able to determine an index (or indices) of either CSI-RS orWBRS. The UE may now determine the remaining index (or indices) of aWBRS (if the index (or indices) of a CSI-RS was previously determined)or a CSI-RS (if the index (or indices) of a WBRS was previouslydetermined). As a result, the UE obtains a beam index per BFRS. The beamindex may be represented by BFRS resource index m (an integer value); orin other words, CSI-RS resource index m in case of the BFRS includingCSI-RSs only, WBRS resource index m in case of the BFRS including WBRSsonly. It is noted that the UE may obtain more than one beam index. Insuch a situation, the indices are denoted m1, m2, and so on. The m-thBFRS resource out of M possible WBRS resources is the best (in terms ofsignal quality, for example) from the point of view of the UE and may beused by the access node to rebuild the DL control channel or to assistin beam management.

The UE optionally selects a BRACH preamble (block 813). In a situationwhere the UE is configured with one or more BRACH preambles, the UEselects one out of the one or more BRACH preambles. In a situation wherethe UE is configured with a unique BRACH preamble that can betransmitted over one or more BRACH channels, the UE selects one out ofthe one or more BRACH channels and transmits the configured preamble.The selection of the one out of the one or more BRACH preambles enablesthe UE to implicitly signal information without having to explicitlysignal the information. As an example, if there are four BRACH preamblesin the one or more BRACH preambles, the UE is able to implicitly signaltwo bits of information through the transmission of one of the fourBRACH preambles. As another example, if there are four BRACH channelsavailable for the UE to send one BRACH preamble, the UE is able toimplicitly signal two bits of information through transmission of thepreamble on one of the four BRACH channels. In either case, the 2-bitinformation can be used by the UE to convey the identified new beamindex m.

The UE, utilizing the relationship or association between the m-th BRACHresource and the m-th BFRS resource to determine the m-th BRACHresource, sends a BRACH preamble on the m-th BRACH resource (block 815).The m-th BRACH resource corresponds to the m-th BFRS resource index asdetermined by the UE as the best WBRS beam and the relationship orassociation between the BRACH and BFRS resources. The sending of theBRACH preamble on the m-th BRACH resource (selected due to itsrelationship with the m-th BFRS resource) affords the UE an excellentchance that the BRACH preamble will successfully arrive at the accessnode, thereby reducing the latency of the beam recovery process.

The UE receives a response, e.g., a BFR response, in a BRACH response(block 817). The response may optionally include an UL grant to allowthe UE to transmit a follow up (or extra) message including a report ofextra information, e.g., a subset of a beam index, beam qualityinformation, etc. The response may be received on a physical downlinkshared channel (PDSCH) or a physical downlink control channel (PDCCH) ora broadcast channel. The response may be addressed with an identifieridentifying the BRACH preamble (or the access node may directly send outthe BRACH preamble). The response may also include a timing alignmentinstruction to synchronize subsequent UL transmissions from the UE. Theresponse may be received in a timing window, potentially with a receivecombiner associated with the transmit precoder used to transmit theBRACH preamble. The timing window the UE uses to receive the responsecorresponds to a BRACH resource used to transmit the BRACH preamble. TheUE may send extra information (e.g., a subset of a beam index, beamquality information, etc.) in accordance with the UL grant (block 819).Alternatively, the UE is able to transmit the BRACH preamble togetherwith the extra information (e.g., a subset of a beam index, beam qualityinformation, etc.). In this situation, the UL grant in the response isnot necessary.

FIG. 9 illustrates a diagram 900 highlighting UE communications in beamrecovery. Diagram 900 displays a BRACH region 905 where the UE sends aBRACH preamble on one or more BRACH resources. As an example, the UEsends the BRACH preamble using an UL transmit beam 907. Diagram 900 alsodisplays a response region 910 where the UE receives a response (such asa BFR response) from an access node. As an example, the UE receives aresponse using a DL receive beam 912 within a time window that isconfigured by the access node. Such a configuration of the time windowmay be specified in terms of the time window starting position, timewindow ending position, time window duration, and so on, for example. Asanother example, such a configuration of the time window may bespecified in a technical standard, or signaled in a RRC message, MAC-CEmessage, DCI message, or a combination thereof.

FIG. 10A illustrates a flow diagram of example operations 1000 occurringin an access node participating in beam recovery using a BFRS thatincludes one or more reference signals, e.g. CSI-RS only, SS only, orCSI-RS and SS. Operations 1000 may be indicative of operations occurringin an access node as the access node participates in beam recovery usinga beam failure RS that includes one or more reference signals, e.g.,CSI-RS only, or SS only, or both CSI-RS and SS.

Operations 1000 begin with the access node configuring BRACH preamblesequences (block 1005). The access node may configure a unique BRACHpreamble sequence for each UE. Alternatively, multiple BRACH preamblesequences may be assigned to a single UE. Alternatively, a single BRACHpreamble sequence may be assigned to multiple UEs. The access node alsosends information about the BRACH preamble sequences to the UEs. Theaccess node optionally sends relations or associations (e.g., in a RRCmessage, a MAC-CE message, a DCI message, or a combination thereof)between BFRS resources (e.g., CSI-RS resources only, SS resources only,or both CSI-RS and SS resources) and BRACH resources, as well as BRACHresponse resources, to the UEs (block 1007). The relations orassociations between the BFRS resources and the BRACH resources (as wellas the BRACH response resources) may assist the UE in determining whichBRACH resource to use to transmit a BRACH preamble, and potentially,which BRACH response resource to receive a response to the BRACHpreamble. The relations or associations between the BFRS resources andthe BRACH resources may enable a UE to identify the time or frequencylocation of the former from the time or frequency location of thelatter, or vice versa. In other words, if the UE identifies a first BFRSresource index, then the relations or associations allows the UE todetermine a first BRACH resource at a first time-frequency location beused by the UE to transmit a first BRACH preamble sequence; and if theUE identifies a second BFRS resource index, then the relations orassociations allows the UE to determine a second BRACH resource at asecond time-frequency location be used by the UE to transmit a secondBRACH preamble sequence; and so on and so forth.

The access node sends spatial-quasi-co-located (SQCL) information (orrepresentations thereof) to the UEs (block 1009). SQCL defines arelationship between two reference signals or data signals such that thetwo signals may be viewed as possessing similar characteristics. TheSQCL information may include associations between CSI-RS resources andSS signals. As an example, in a one to one SQCL association, each CSI-RSsignal is associated with one SS signal such that the transmit precoderfor the CSI-RS signal is the same as a transmit precoder for the SSsignal. It is possible that multiple CSI-RS signals are associated witha single SS, and vice versa. The SQCL information may be signaled to theUE from the access node in a RRC message, a MAC-CE message, a DCImessage or a combination thereof, and stored in tabular form or in amemory of the UE. The access node sends the BFRS, including the CSI-RS,WBRS, or CSI-RS and WBRS, for example, using DL transmit beams (block1011). One potential purpose of signaling the SQCL information may be toenable to UE to find a proper WBRS signal based on the detected BFRSwhen the BFRS does not include a WBRS, for example. As an example, if aCSI-RS (as a component of a BFRS) signal is detected, then the WBRS thatis SQCLed with this particular CSI-RS may be identified; and if a WBRS(as a component of a BFRS) is detected, then the WBRS itself (which isof course SQCLed with itself) may be identified. In other words,independent of if the detected BFRS signal is a CSI-RS, a WBRS, or both,a proper WBRS may be identified based on the SQCL information.

The access node receives a BRACH preamble from a UE that has experienceda beam failure (block 1013). The BRACH preamble is received on a BRACHresource associated with an m-th WBRS. Furthermore, the BRACH preamblemay be received on an UL receive beam of the access node that is beamcorrespondent to a DL transmit beam of the access node used to transmitthe m-th WBRS. In general, the access node monitors all BRACH resourcesfor BRACH preambles. The access node identifies the UE (block 1015). Theaccess node may compare received signals on the multiple BRACH resourcesand determine which UE requested beam recovery (by analyzing thereceived BRACH preamble and BRACH preamble to UE assignments, forexample). In a situation where the UE is assigned more than one preamblesequence which can be transmitted on a BRACH channel, the access nodeanalyzes which sequence is being transmitted by the identified UE anddetects the intended beam index of the CSI-RS or WBRS. In a situationwhere the UE is assigned one preamble sequence which can be transmittedon more than one BRACH channel, the access node analyzes which channelis being used by the identified UE to transmit the preamble sequence anddetects the intended beam index of the CSI-RS or WBRS. In a situationwhere the access node receives multiple BRACH preambles from a singleUE, the access node may determine which BRACH resource provided the bestquality, potentially conveying to the access node which responseresource to transmit a response, such as a BFR response. The access nodemay be able to identify the UE in accordance with the BRACH preamble,for example. The access node may generate an UL resource grant for theUE (block 1017). The UL resource grant is for resources that allow theUE to transmit further recovery information to the access node. Thefurther recovery information may include the extra recovery informationdiscussed previously (such as in the discussion of FIG. 6), as well aschannel quality information, such as SNR, SINR, RSRP, RSRQ, RSSI, and soon. The access node sends a response, such as a BFR response, possiblywith the UL resource grant (or information related thereto) to the UE(block 1019). The response may be sent on a PDSCH or a PDCCH or abroadcast channel. The response may be addressed using an identifieridentifying the detected BRACH preamble or the access node may send thedetected BRACH preamble directly. The access node receives an ULtransmission from the UE (block 1021). The UL transmission may, forexample, include the further recovery information, such as one or moreCSI-RS indices n, from the UE, or beam quality information, from the UE.The access node rebuilds a DL control channel or assists in beammanagement (block 1023). The access node utilizes the recoveryinformation provided by the UE to rebuild the DL control channel orassist in beam management (UL or DL) in a subsequent period.Alternatively blocks 1017 and 1019 may be omitted, which means thatblocks 1013 and 1021 may be performed in a single transmission.

FIG. 10B illustrates a flow diagram of example operations 1050 occurringin a UE participating in beam recovery where the UE monitors one or morereference signals. Operations 1050 may be indicative of operationsoccurring in a UE as the UE participates in beam recovery where the UEmonitors only one reference signal, e.g., CSI-RS only, WBRS only, orboth CSI-RS and WBRS.

Operations 1050 begin with the UE receiving a BRACH preamble sequenceconfiguration from an access node (block 1055). The UE optionallyreceives relations or associations between BFRS resources (CSI-RSresources only, SS resources only, both CSI-RS and SS resources) andBRACH resources, as well as BRACH response resources from the accessnode (block 1057). The relations or associations between the BFRSresources and the BRACH resources (as well as the BRACH responseresources) may assist the UE in determining which BRACH resource to useto transmit a BRACH preamble based on the detected BFRS or theidentified WBRS, and potentially, which BRACH response resource toreceive a response to the BRACH preamble. The UE receives SQCLinformation (block 1059). The SQCL information includes associationsbetween CSI-RS and SS signals. The SQCL information may be used by theUE to determine CSI-RS beam indices from WBRS beam indices, anddetermine WBRS beam indices from WBRS beam indices, for example. As anexample, in a one-to-one association, each CSI-RS signal is associatedwith one WBRS signal. It is possible that multiple CSI-RS signals areassociated with a single WBRS, and vice versa. The SQCL information maybe signaled to the UE in a RRC message, a MAC-CE message, a DCI message,or a combination thereof, and stored in tabular form or in a memory ofthe UE.

The UE monitors the BFRS signals (CSI-RS or WBRS signals in general) anddetermines index (indices) of best, in terms of quality, for example,CSI-RS beam(s) or WBRS beams (block 1061). As a result, the UE obtains abeam index per CSI-RS, or a beam index per WBRS. The beam index may berepresented by CSI-RS resource index n (an integer value), or WBRSresource index m. It is noted that the UE may obtain more than one beamindex.

The UE determines index (indices) of the best WBRS beam(s) (block 1063).It is noted that if the detected beam is a WBRS signal with best WBRSresource index m, then the identified beam is simply the best WBRSresource index m itself. It is noted that if the detected beam is aCSI-RS signal with best CSI-RS resource index n, the UE makes use of theSQCL information to determine the index m of the best WBRS beam(s) fromthe CSI-RS beam index n. It is noted that the UE may obtain multiplebeam indices of the best BFRS beams when the UE obtains multiple beamindices. The m-th WBRS resource out of M possible WBRS resources may bethe best from the point of view of the UE (in terms of quality, forexample) and may be used by the access node to rebuild the DL controlchannel and to assist in beam management.

The UE optionally selects a BRACH preamble (block 1065). In a situationwhere the UE is configured with more than one BRACH preambles, the UEselects one out of the more than one BRACH preambles. The UE, utilizinga relationship between the m-th BRACH resource and the m-th WBRSresource to determine the m-th BRACH resource, sends a BRACH preamble onthe m-th BRACH resource or region (block 1067). The m-th BRACH resourcecorresponds to the m-th WBRS resource index as determined by the UE asthe best WBRS beam and the relationship between the BRACH and WBRSresources. The sending of the BRACH preamble on the m-th BRACH resourceaffords the UE an increased chance that the BRACH preamble willsuccessfully arrive at the access node (due to using a resourceassociated with the best quality beam or resource, for example), therebyreducing the latency of the beam recovery process.

The UE receives a response, such as a BFR response (block 1069). Theresponse may include an UL grant to allow the UE to transmit a follow upmessage (on a physical uplink shared channel (PUSCH), for example)including a report of a CSI-RS beam index, for example. The response maybe received on a PDSCH or a PDCCH or a broadcast channel. The responsemay be addressed with an identifier identifying the BRACH preamble (orthe access node may directly send out the BRACH preamble). The responsemay also include a timing alignment instruction to synchronizesubsequent UL transmissions from the UE. The response may be received ina timing window, potentially with a receive combiner associated with thetransmit precoder used to transmit the BRACH preamble. The timing windowthe UE uses to receive the response corresponds to a BRACH resource usedto transmit the BRACH preamble. The UE monitors all timing windows, witheach timing window corresponding to one of the BRACH resources used totransmit the BRACH preamble for the response. The UE sends one or moreCSI-RS resource indices n in accordance with the UL grant (block 1071),if the UL grant is included in the BFR response.

FIG. 11 illustrates a diagram 1100 highlighting an example BRACHpreamble transmission and response reception on multiple resources. Asshown in FIG. 11, a BFRS region 1105 presents BFRS resources and accessnode DL transmit beams used to transmit BFRS, a BRACH region 1107presents BRACH resources (e.g., BRACH resources 1116, 1118, and 1120)and UL receive beams (e.g., beams 1110, 1111, and 1112) used to receiveBRACH preambles and UL transmit beams (e.g., beams 1115, 1117, and 1119)used to transmit BRACH preambles, and a response region 1109 presentsresponse resources (e.g., response resources 1122, 1124, and 1126) andUL receive beams (e.g., beams 1121, 1123, and 1125) used to receiveresponses, such as BFR responses. Multiple beams and resources may beused to increase the likelihood that the BRACH preambles or responsesare successfully received. It is noted that the associations orrelations between BRACH resources and BFRS resources are maintained in asituation when multiple beams and resources are used.

FIG. 12 illustrates a diagram 1200 highlighting the sending of a BRACHpreamble and the detection of a response. As shown in FIG. 12, the UEsends a BRACH preamble on one or more BRACH resources 1205. However, theUE monitors timing windows associated with all of the BRACH resources toensure that the response is received 1210.

In summary, a UE initiating a beam recovery:

-   -   Detects a BFRS resource index, may be CSI-RS resource, SS        resource, or both;    -   Identifies a WBRS resource index m based on SQCL information        between CSI-RS and SS;    -   Sends a BRACH preamble on a m-th BRACH resource in a BRACH        region;    -   Monitors for responses in a response region to receive a        response;    -   May send a message with extra recovery information, such as one        or more CSI-RS indices n;    -   May monitor a DL control channel, the DL control channel and the        one or more CSI-RS indices n may be spatially QCLed.

In summary, the access node participating in beam recovery receives ordetermines the following information:

-   -   Information A: identity of the UE requesting beam recovery;    -   Information B (n): an identified or reported CSI-RS resource or        beam index (CRI) used by the access node to rebuild a DL control        channel. The CRI may comprise two parts,        -   B1—WBRS index (or indices),        -   B2—CSI-RS index (or indices) with a group of multiple            CSI-RSs that is spatially QCLed with a WBRS with WBRS index            (or indices). B2 is referred to as an intra-group index.        -   With B1 and B2, it is possible for the access node to            reconstruct B. It is noted that CSI-RS and WBRS may be two            subsets of BFRS. Thus the two-part information may be            signaled altogether, rather than individually, as an index            of BFRS. Here, the set of BFRS signals may be simply viewed            as a combination (such as union, concatenation, etc.) of            CSI-RS signals and WBRS signals.

FIG. 13 illustrates a diagram 1300 of example beams for SS and CSI-RS.As shown in FIG. 13, a precoder for an example SS has beam footprint1305, while precoders for example CSI-RS1, CSI-RS2, CSI-RS3, and CSI-RS4have beam footprints 1310, 1312, 1314, and 1316, respectively. Fordiscussion purposes, let an index of a CSI-RS1 be n, an index of SS bem, and an intra-group index of CSI-RS1 in a CSI-RS group associated withSS be i. Then, if indices m and i are known (e.g., reported by the UE),it is possible to determine n. Similarly, if indices n and m are known,it is possible to determine i. Furthermore, if indices n and i areknown, it is possible to determine m. It is noted that in FIG. 13, SS isintended to be an example of a WBRS.

In a first example embodiment, the access node configures a UE specificpreamble sequence for each UE. A UE initiating beam recovery may sendits UE specific preamble sequence, which is detected by the access node.The access node will be able to determine the identity of the UE thatsent the UE specific preamble, thereby obtaining information A. The UEsends the CRI using the UL grant, thereby directly providing the CRI tothe access node, thereby providing information B to the access node.

In a second example embodiment, the access node configures a UE specificpreamble sequence for each UE. A UE initiating beam recovery may sendits UE specific preamble sequence, which is detected by the access node.The access node will be able to determine the identity of the UE thatsent the UE specific preamble, thereby obtaining information A.Furthermore, the access node is able to determine which BRACH resourceconveyed the UE specific preamble, thereby obtaining information B1,which is the identified SS resource index m based on the detected CSI-RSresource index n if a CSI-RS resource index is detected, or theidentified resource index m itself if a SS resource index is detected.The UE may send out the intra-group index using the UL grant, therebyproviding information B2 to the access node. The access node may useinformation B1 and B2 to determine information B. If the intra-groupindex i is not sent, the access node may use information B1 (which isthe identified SS resource index m) directly.

In a third example embodiment, the access node configures a group of UEspecific preamble sequences for each UE. All of the preambles within thegroup are associated with a single UE. A UE initiating beam recovery maysend a UE specific preamble sequence from its group of UE specificpreamble sequences. The access node detects the UE specific preamblesequence, determines the group of UE specific preamble sequences fromthe UE specific preamble and determines the identity of the UE that sentthe UE specific preamble, thereby obtaining information A. In oneexample, the access node is able to determine which BRACH resourceconveyed the UE specific preamble, thereby obtaining information B1.Additionally, the access node is able to determine which preamblesequence within the group of UE specific preamble sequences the UEspecific preamble is and infer the intra-group index of the UE specificpreamble, thereby obtaining information B2. The access node usesinformation B1 and B2 to determine information B. In another embodiment,the access node is able to determine information B directly by analyzingwhich preamble sequence is being used by the identified UE and whichBRACH resource conveyed the preamble sequence. It is noted that in thiscase, the access node and UE agree a priori on which combination of UEpreamble sequence and BRACH resource corresponds to which beam index.This can be done in advance by the access node sending out a mappingtable between each beam index and the corresponding combinations orassociations of UE preamble sequence and BRACH resource, for example.

In a fourth example embodiment, the access node configures a UE specificpreamble sequence for each UE. A UE initiating beam recovery may sendthe UE specific preamble sequence, which is detected by the access node.The access node will be able to determine the identity of the UE thatsent the UE specific preamble, thereby obtaining information A.Furthermore, the access node is able to determine which BRACH resourceconveyed the UE specific preamble, thereby obtaining information B1. TheUE sends another sequence before or after the UE specific preamblesequence at a pre-determined location. The other sequence conveys theintra-group index and was agreed upon a priori between the UE and theaccess node or specified by a technical standard or operator. The accessnode determines which other sequence is sent, thereby obtaininginformation B2. The access node uses information B1 and B2 to determineinformation B.

In another embodiment, the access node is able to determine informationB directly by analyzing which sequence is being used by the identifiedUE and which BRACH resource conveyed the preamble sequence. It is notedthat in this case, the access node and UE agree a priori on whichcombination of UE preamble sequence and BRACH resource corresponds towhich beam index. This can be done in advance by the access node sendingout a mapping table between each beam index and the correspondingcombinations or associations of UE preamble sequence and BRACH resource.

In a fifth example embodiment, the access node configures a UE specificpreamble sequences for each UE and for each direction, assigns multipleBRACH sub-channels (potentially in the frequency domain) for each UE. Itis noted that there are multiple BRACH opportunities in the time domainwith each BRACH opportunity corresponding to a potentially differentWBRS direction. A UE initiating beam recovery may send a UE specificpreamble sequence on one sub-channel (in the frequency domain, forexample) and one opportunity (in the time domain, for example). Theaccess node detects the UE specific preamble sequence, and the BRACHsub-channel, and determines the identity of the UE that sent the UEspecific preamble, thereby obtaining information A. It is noted that theaccess node may assign L sub-channels overall. It is possible that eachUE is able to use any of the L sub-channels. It is also possible thateach UE is able to use only part, such as L1, of the L sub-channels.Such restriction may be signaled by the access node to the UE in advancein, e.g., a RRC message. If each of the UE is able to use all Lsub-channels, then the access node can analyze the BRACH sub-channels todetect part of the information B, but may not be able to detect the UEidentity A. If each of the UE is able to use only part of the Lsub-channels, then the access node can analyze the BRACH sub-channel todetect part of the information B, as well as to detect part of the UEidentity A. In one example, the access node is able to determine whichBRACH opportunity conveyed the UE specific preamble, thereby obtaininginformation B1. Additionally, the access node is able to determine whichBRACH sub-channel is being used by the identified UE and infers theintra-group index of the UE specific preamble, thereby obtaininginformation B2. The access node uses information B1 and B2 to determineinformation B. Alternatively, the access node is able to determineinformation B directly by analyzing which BRACH opportunity is beingused in the time domain and which BRACH sub-channel is being used in thefrequency domain by the identified UE. It is noted that in this case,the access node and UE agree on which combination or association ofBRACH opportunity in the time domain and BRACH sub-channel in the timedomain corresponds to which beam index. This can be done in advance bythe access node sending out a mapping table between each beam index andthe corresponding combinations or associations of BRACH opportunity inthe time domain and BRACH sub-channel in the frequency domain.

Table 1 provides a summary of the four example embodiments.

TABLE 1 Summary of example embodiments. Second Third Fourth Firstembodiment embodiment embodiment embodiment Sequence, grant, FormerFormer Latter Latter or grant-based reporting versus purely sequencebased reporting Determine UE Preamble Preamble Preamble Preambleidentity based on sequence sequence sequence sequence Report of nExplicit, grant Not explicit Not explicit Not explicit based reportReport of m Not needed Implicit, based Implicit, based Implicit, basedon BRACH on BRACH on BRACH position position position Report of i Notneeded Explicit, grant Implicitly in Implicitly in based report preamblepreamble

As discussed previously, QCL defines a relationship between tworeference signals or data signals such that the two signals may beviewed as possessing similar characteristics. Example characteristicsinclude carrier frequency, time offset, frequency offset, spatialprecoding vectors, and so on. SQCL is a category of QCL with twoprecoded or beamformed signals that are precoded using the same orsimilar precoder. As an illustrative example, a first signal SIG1 (areference signal or data signal, for example) and a second signal SIG2(a reference signal or data signal, for example) are spatially QCLed ifthey are transmitted using the same precoder. In other words,

X1=Precoder*SIG1; X2=Precoder*SIG2,

where X1 is the precoded SIG1 and X2 is the precoded SIG2 and SIG1 andSIG2 are the first signal and the second signal without precoding,respectively.

FIG. 14 illustrates a graphical representation 1400 of two precodersthat are spatially QCLed. A first beam pattern 1405 represents aprecoder for a first signal and a second beam pattern 1410 represents aprecoder for a second signal. The beam patterns overlap because the twoprecoders are identical.

According to an example embodiment, techniques for identifying beamsusing a one-to-many mapping of beams are provided. The techniquesidentify a first beam using a one-to-many mapping of first beams tosecond beams when one of the second beams is known, and vice versa. Asan illustrative example, in a communications system with one or morefirst beams and one or more second beams and multiple one-to-manymappings of first beams to second beams, as long as any two or morefirst beams do not map to the same second beam, once a second beam(e.g., CSI-RS beam) is identified, it is possible to determine the firstbeam (e.g., WBRS beam) that maps to the second beam using a one-to-manymapping.

Let a first beam be a precoded signal SIG0 that is precoded withprecoder P_0, and one or more second beams be a set of N precodedsignals SIG1, . . . , SIGN that are precoded with precoders P_1.1, . . ., P_1.N. The first beam and the one or more second beams are said tohave a one-to-many mapping if the beam patterns of the precoders P_1.1,. . . , P_1.N lie within the beam pattern of precoder P_0. Beams of aone-to-many mapping are said to have a one-to-many SQCL (OMSQ)relationship. FIG. 15 illustrates a diagram 1500 of beam patterns ofprecoders for a first beam and one or more second beams, where theprecoders have an OMSQ relationship. As shown in FIG. 15, N is equal tofour. A first beam pattern 1505 represents a precoder P_0 for the firstbeam, while beam patterns 1510, 1512, 1514, and 1516 represent precodersP_1.1, . . . , P_1.4 for each second beam in the plurality of secondbeams.

With respect to a relationship between precoders P_0 and {P_1.1, . . . ,P_1.N}, consider a virtual signal X1, which comprises a signal S that isprecoded with P_1.1, . . . , P_1.N altogether at the same time (asopposed to being N signals that are separately precoded with P_1.1, . .. , P_1.N, respectively, one signal at a time), and a precoded signal X0that comprises the signal S precoded with P_0. Virtual signal X1comprises X_1.1, . . . , X_1.N, where X_1.1 is the signal S precodedwith precoder P_1.1, and X_1.N is the signal S precoded with precoderP_1.N. If the virtual signal X1 and the precoded signal X0 are the same(within a tolerable difference between precoders P_0 and {P_1.1, . . . ,P_1.N} as defined by a technical standard), then precoders P_0 and{P_1.1, . . . , P_1.N} have an OMSQ relationship. Similarly, virtualsignal X1 and signal X0 have an OMSQ relationship. It is noted that inthe example presented herein, the signal X0 (or precoder P_0) is the oneand the virtual signal X1 (or precoders {P_1.1, . . . , P_1.N}) are themany of the one-to-many mapping.

It is noted that the precoders {P_1.1, . . . , P_1.N} are typicallydifferent from one another. Hence, there is no QCL relationship betweenthe precoders {P_1.1, . . . , P_1.N}. However, a typical relationshipbetween the precoders {P_1.1, . . . , P_1.N} may be that theirrespective beam patterns are adjacent to one another in terms of theirbeam footprints.

It is noted that a relationship between precoder P_0 and any one of theprecoders {P_1.1, . . . , P_1.N} (or signal X0 and any one of signalsX_1.1, . . . , X_1.N) is that the beam pattern of signal X0 spans abroader angle range than the beam pattern of any one of signals X_1.1, .. . , X_1.N. Furthermore, the signal X0 and any one of signals X_1.1, .. . , X_1.N are correlated. Signals that have an OMSQ relationship arealso said to be correlated. FIG. 16 illustrates a diagram 1600 of beampatterns of precoded signals, highlighting potential relationships.Diagram 1600 includes beam patterns for signal X_0 1605, signal X_1.11610, and signal X_2 1615. As shown in FIG. 16, signal X_0 and signalX_1.1 are correlated, but signal X_2 (which was precoded using adifferent precoder) is not correlated with either signal X_0 or X_1.1.In some cases, the signaling of the OMSQ relationship between signal X_01605 and X_1.1 1610 provides the receiver guidance in choosing areceiver (e.g., receiver combiner). For example, the OMSQ relationshipsuggests that the receiver used for X_0 1605 may be used to receiveX_1.1 1610, and vice versa. On the other hand, the OMSQ relationshipsuggests that the receiver used for X_2 1615 may not be used toeffectively receive X_1.1 1610.

According to an example embodiment, the OMSQ relationship is used toidentify alternate signals usable in communications. As an illustrativeexample, if a first signal has become unavailable or unreliable, it ispossible to identify an alternate signal using an OMSQ relationshipbetween the first signal and one or more second signals. The alternatesignal (one of the one or more second signals) may be used in place ofthe first signal.

As an illustrative first example, consider a situation where atransmitting device is sending reference signals X_0 1605, X_1.1 1610,and X_2 1615. The transmitting device may convey that signals X_0 1605and X_1.1 1610 have an OMSQ relationship or that signals X_0 1605 and{X_1.1, . . . , X_1.N} have an OMSQ relationship. A receiving device mayinitially use information in signal X_1.1 1610. However, signal X_1.11610 becomes unreliable or unavailable and the receiving device is nolonger able to reliably receive signal X_1.1 1610. The receiving devicemay utilize the OMSQ relationship between signals X_0 1605 and X_1.11610 and use signal X_0 1605 as a backup for signal X_1.1 1610. It isnoted that because signals X_0 1605 and X_2 1615 do not have an OMSQrelationship (or at least the transmitting device did not provideinformation that the two signals have an OMSQ relationship), thereceiving device would not use signal X_2 1615 as a backup for signalX_0 1605.

As an illustrative second example, consider a situation where atransmitting device is sending reference signals X_0 1605, X_1.1 1610,and X_2 1615. The transmitting device may provide information conveyingthat signals X_0 1605 and X_1.1 1610 have an OMSQ relationship or thatsignals X_0 1605 and {X_1.1, . . . , X_1.N} have an OMSQ relationship.The transmitting device may signal a receiving device that is currentlyreceiving signal X_1.1 1610 that the transmitting device will begin touse a higher level signal (signal X_0 1605) instead. The transmittingdevice, knowing the OMSQ relationship between signals X_0 1605 and X_1.11610, begins to receive signal X_0 1605 instead of signal X_2 1615because signals X_2 1615 and signal X_1.1 1610 do not have an OMSQrelationship.

It is noted that the discussion presented above focusses mainly in theangle domain. There may be a power difference (due to a difference oftransmit power or precoding gain, for example) between the one signal(e.g., signal X_0 1605) and the many signals (e.g., signals {X_1.1, . .. , X_1.N}) that are aggregated. The transmitting device may sendadditional signaling including a power difference between the one signaland the many signals (it is assumed that the transmit power is equal foreach of the many signals).

FIG. 17 illustrates a flow diagram of operations 1700 occurring in anaccess node utilizing OMSQ relationships to change beams. Operations1700 may be indicative of operations occurring in an access node as theaccess node uses OMSQ relationships to change beams.

Operations 1700 begin with the access node sending OMSQ relationshipinformation to UEs (block 1705). During normal operations, the accessnode performs a check to determine if a beam change is warranted (block1707). The beam change may be warranted if one or more UEs providefeedback regarding the quality of the beams have dropped below athreshold, for example. As another example, a beam change may bewarranted if the access node receives a BRACH preamble conveyinginformation about an occurrence of a beam failure. If the beam change isnot warranted, the access node continues to send signals on beams (block1715).

However, if the beam change is warranted, the access node selects analternate beam in accordance with the OMSQ relationship information(block 1709). The access node optionally triggers the use of thealternate beam (block 1711). The access node may send information aboutan index of the alternate beam, for example. The access node sendssignals on the alternate beam (block 1713). The access node may alsosend information regarding an operation of default beam switch only,i.e., switching the transmit beam from the current transmit beam to adefault backup beam (of the current transmit beam). In this case, signalX_0 1605 is the default backup version of signal X_1.1 1610, forexample. This may trigger the UE to switch to a receiver for the defaultbackup beam X_0 1605.

FIG. 18 illustrates a flow diagram of operations 1800 occurring in a UEutilizing OMSQ relationships to change beams. Operations 1800 may beindicative of operations occurring in a UE as the UE uses OMSQrelationships to change beams.

Operations 1800 begin with the UE receiving OMSQ relationshipinformation from an access node (block 1805). During normal operations,the UE performs a check to determine if a beam that it is receiving hasbecome unreliable (or unavailable) (block 1807). As an example, a beammay be deemed as unreliable if a signal quality associated with the beamdrops below a threshold. As another example, if one or more decodingattempts of transmissions using the beam fail, the beam may be deemed asunreliable. As an example, a beam may be deemed unavailable if the UEcan no longer detect signals on the beam. If the beam remains reliable,the UE continues to receive signals on the beam (block 1813).

If the beam has become unreliable (or unavailable), the UE selects analternative beam in accordance with the OMSQ relationship information(block 1809) and receives signals on the alternative beam (block 1811).The UE may change its receive precoder to one associated with thealternative beam to begin receiving signals on the alternative beam, forexample. Alternatively, if the UE receives information specifying the UEto use an alternative beam, the UE begins to receive signals on thealternative beam, independent of the reliability or unreliability of thebeam.

In this disclosure, the focus has mainly been on sending a beam failurerecovery request using a random access channel BRACH that is potentiallydifferent from a PRACH channel in time or frequency locations within thefrequency band (category B). In co-assigned applications: docket numbersHW85458110US01 entitled “Method for Response to PUCCH-based Beam FailureRecovery Request” and HW85457640US01 entitled “System and Method forBeam Failure Recovery Request Reporting”, which are hereby incorporatedherein by reference, two other methods of transmitting the request apresented, one based on sending the request via scheduling request whichis a special message carried over PUCCH channel (category P1), the otherbased on sending the non-status report (SR)-request over a PUCCH channel(category P2).

It remains unclear when different methods are supported (e.g., bothcategory B and category P1, both category B and category P2, or allcategories B, P1 and P2 are supported), how does the UE choose whichmethod to use. For discussion purposes, suppose that both category B andcategory P are supported and that category P can be either category P1,or category P2, or both categories P1 and P2.

It is noted that the time and frequency locations of the category Bchannel (i.e., the BRACH channel resources) and the category P channel(i.e., either the PUCCH channel resources carrying SR for P1 or thePUCCH channel resources carrying non-SR for P2) should be determined orconfigured in advance. From the point of view of the UE, it can transmita BRACH preamble sequence on a category B channel resource, or it cantransmit a PUCCH content (SR or non-SR) on a category P channelresource. The UE cannot, and should not transmit a BRACH preamblesequence on a category P channel resource, nor should the UE transmit aPUCCH content (SR or non-SR) on a category B channel resource.

For the category B channel resource, there is the category B responseresource where the UE can monitor to listen for responses for anypreamble sequence transmission on the category B channel resource. Forthe category P channel resource, there is the category P responseresource where the UE can monitor to listen for responses for any PUCCHtransmission (SR or non-SR) on the category P channel resource.

It is noted that before the UE actually does send a response, such as aBFR response, on the category B channel, the UE should already know whenit expects to receive a response by monitoring the category B responseresource within a certain time window of size W1, starting from a timeinstance T1 later. Similarly, before the UE actually sends a response onthe category P channel, the UE should already know when it expects toreceive a response by monitoring the category P response resource withina certain time window of size W2, starting from a time instance T2later.

There may be two possibilities in terms of whether the UE has fullauthority in determining which channel to use to send the response.

The UE having full authority in determining which channel to use to sendthe response may be configured by the access node. In one embodiment,the access node may configure in advance (using a message) telling theUE that it should either always use a category B channel, a category P1channel, or a category P2 channel, or a prioritization of category B,P1, or P2 channels (the UE should use a category B channel first if acategory B channel is given a higher priority than P1 or P2 channels).

In another embodiment, the access node may configure in a message (orspecified by a technical standard) that the UE may use a category Pchannel (and the associated method to send requests) only if the UE isnon-beam-correspondent.

In another embodiment, the access node may configure in a message (orspecified by a technical standard) that the UE may use a category Pchannel (and the associated method to send requests) only if the UEknows that its uplink control channels and downlink control channels arenot reciprocal. For example, the UE may infer that the uplink ordownlink channels are not reciprocal by comparing its transmit beams ofthe uplink control channels and receive beams of the downlink controlchannels and find them to be significantly different from each other.The access node may also send a message to the UE on whether the receivebeams of the uplink control channels (at access node side) and thetransmit beams of the downlink control channels (at access node side)are the same or different, based upon which UE may infer whether thedownlink control and uplink control channels are reciprocal or not.

In another embodiment, the access node may configure in a message (orspecified by a technical standard) that the UE may use a category Pchannel (and the associated method to send request) if the carrier ofthe category P channel is different from the carrier associated with thebeam failure.

In another embodiment, the access node may configure in a message (orspecified by a technical standard) that the UE may use a category Pchannel (and the associated method to send request) if the UE hasidentified a new beam or not.

Alternatively, the UE may have its own say in choosing which channel touse to send the BFR response.

In one embodiment, the UE may choose which ever channel (category Bchannel or category P channel) depending on whichever channel resourcearrives first, in the hope to recover from the beam failure as soon aspossible.

In another embodiment, the UE may choose which ever channel depending onwhichever response should arrive first (based on the knowledge of W1,T1, W2, T2, for example), in the hope to recover from the beam failureas soon as possible.

In another embodiment, the UE may choose whichever channel depending onwhether the UE has identified a new candidate beam. For example, the UEmay choose to transmit on a category B channel (and the associatedmethod to send request) if it identifies a new candidate beam, or if itidentifies no new candidate beam.

In another embodiment, the UE may choose whichever channel depending onits own knowledge of whether the uplink or downlink control channels arereciprocal. For example, the UE may choose to transmit on a category Bchannel (and the associated method to send request) if it infers thatthe downlink control and uplink control channels are not reciprocal, orif the UE is non-beam-correspondent.

If the UE has used category P channel resources to send responses andcontinue to monitor the category P response resources, and finds nopositive response therein, then the UE should use category B channelresources to send responses.

If the UE has used category B channel resources to send responses andcontinue to monitor the category B response resources, and finds nopositive response therein, then the UE should use category P channelresources to send beam failure requests.

If the UE has used category P channel resources to send responses andsees category B channel resources become available before the category Presponse resources arrive, then the UE should use category B channelresources to send responses.

If the UE has used category B channel resources to send responses andsees category P channel resources become available before the category Bresponse resources arrive, then the UE should use category P channelresources to send responses.

If the opportunity for UE to use category B and category P channelresources arrive at substantially the same time, UE may select aresource (e.g., the category B or the category P channel resources) totransmit a response based on a preconfigured priority between category Band category P channel resources. If UE capability allows, UE may alsotransmit a response by using both category B and category P resourcessimultaneously.

FIG. 19 illustrates first example BRACH resources 1900. As shown in FIG.19, BRACH resources 1900 consists of 64 BRACH blocks, such as BRACHblocks 1905, 1907, 1909, and 1911, arranged in the time, frequency, andsequence domain. Each BRACH block is a smallest unit usable by a UE tosend a BRACH preamble to trigger beam failure recovery. Each BRACH blockis unique in terms of time, frequency, and sequence. As an illustrativeexample, an access node allocates four BRACH time opportunities, such asBRACH time opportunity 1915. In a particular BRACH time opportunity, theaccess node allocates four BRACH frequency opportunities (sub-channels),such as sub-channels 1920, 1922, and 1924. For each time-frequencyopportunity, the access node allocates four preamble sequences, whichcorrespond to individual BRACH blocks (such as BRACH blocks 1905, 1907,1909). The example configuration with four BRACH time opportunities,four BRACH frequency opportunities, and four preamble sequences ispresented for discussion purposes only and is not intended to belimiting to either the scope or the spirit of the example embodiments.

It is noted that the access node may allocate to each UE more than oneBRACH frequency opportunity in the frequency domain or more than onepreamble sequence in the sequence domain for beam failure recoverypurposes. Furthermore, although multiple UEs may share the same BRACHfrequency opportunity for transmitting a preamble sequence, differentUEs typically have different preamble sequences for UE identificationpurposes.

According to an example embodiment, an association between a beam indexof a CSI-RS and a block index of a BRACH block is used to allow easyidentification a block index from a beam index or vice versa. This is aspecial case where the BFRS consists of CSI-RS only. The association orrelation between beam indices of CSI-RS and block indices of BRACHblocks enable the identification of one index when the other index isknown. The association or relation may be specified by a technicalstandard, an operator of the communications system, or throughcollaboration between access node and UEs. The association or relationmay be provided to UE during initial attachment to the communicationssystem. Alternatively, the association or relation may be programmedinto the UEs or after being determined through collaborative measures.

According to an example embodiment, an indirect association or relationbetween a beam index a CSI-RS and a block index of a BRACH block is usedto allow easy identification a block index from a beam index or viceversa. The indirect association relates relative indices of the beamindices of CSI-RS to relative indices of block indices of BRACH blocks,relative to a common reference signal, such as a WBRS. The commonreference signal is referred to as a relative reference signal (RRS).Such an indirect CSI-RS to BRACH block association between beam indicesand block indices may be signaled by the access node by RRC signaling,MAC-CE signaling, DCI signaling, or a combination thereof, for example,or specified by a technical standard and stored in the devices.

FIG. 20A illustrates a table 2000 of relative indices of block indicesof an example BRACH block configuration. Table 2000 presents therelative indices of block indices of the BRACH block configuration shownin FIG. 19. Table 2000 includes columns for BRACH index 2005, BRACH timeindex 2007, a BRACH secondary index 2009, BRACH frequency index 2011,and BRACH sequence index 2013. The BRACH secondary index can be viewedas a combination of BRACH frequency index and BRACH sequence index. Itis noted that if there is only one sub-channel available then the BRACHfrequency index is always 1. If there is only one sequence available perUE, then the BRACH sequence index is always 1. Values in BRACH index2005 correspond to an absolute BRACH index, while values in time index2007 correspond to BRACH time opportunities, values in BRACH secondaryindex 2009 correspond to beam indices of CSI-RS beams of a BRACH timeopportunity, values in BRACH frequency index 2011 correspond to BRACHfrequency opportunities, and values in BRACH sequence index 2012correspond to preamble sequence indices. As an example, absolute BRACHindex 25 corresponds to a second BRACH time opportunity, a ninth CSI-RSbeam of the second BRACH time opportunity which happens to occupy athird BRACH frequency opportunity, and preamble sequence A. In general,each of the 64 absolute BRACH indices may be referenced with an m-thprimary WBRS beam index and an i-th secondary CSI-RS beam index, where mis the WBRS index that the BRACH block is correspondent to and i is theBRACH block index within the group of BRACH blocks sharing the same m-thWBRS index.

FIG. 20B illustrates a table 2050 of relative indices of beam indices ofCSI-RS. Table 2050 presents the relative indices of beam indices of theCSI-RS corresponding to BRACH block configuration shown in FIG. 19.Table 2050 includes columns for CSI-RS index 2055, mapped WBRS index2057, and secondary index 2059. Values in CSI-RS index 2055 correspondto absolute beam indices of CSI-RS, while values in mapped WBRS index2057 correspond to WBRS indices corresponding to the CSI-RS beam index,and values of secondary index 2059 correspond to CSI-RS beam indices ofCSI-RS beams relative to the WBRS index. As an example, absolute CSI-RSindex 17 corresponds to a second WBRS beam and a first CSI-RS beamrelative to the second WRBS beam. In general, each of the 64 absoluteBFRS (e.g., CSI-RS) indices may be referenced with an m-th primary BRACHblock index and an i-th secondary BRACH block index, where m is the BFRS(CSI-RS) index that the BFRS (CSI-RS) beam corresponding to the absoluteBFRS (CSI-RS) index is QCLed with and i is the BFRS (CSI-RS) indexwithin a group of BFRSs (CSI-RSs) sharing the same m-th primary BRACHblock index. If the BFRS is a WBRS, then the m-th BFRS index is simplythe WBRS index m itself, and the i-th secondary index is not needed,which is a special case of the above general case.

Tables 2000 and 2050 present a single example indirect associationbetween beam indices and block indices. Other indirect associations arepossible. The access node and the UEs may agree on an indirect CSI-RS orSS to BRACH association so that the UE is able to determine a BRACHblock index based on a CSI-RS index or SS index. Similarly, the indirectCSI-RS or SS to BRACH association enables the access node to determine aCSI-RS index or SS index based on a BRACH block index. The access nodeand UEs may also agree on indirect secondary associations so that the UEcan determine a secondary BRACH block index based on a secondary CSI-RSindex, and the access node can determine a secondary CSI-RS index basedon a secondary BRACH block index. It is noted that each secondary BRACHblock index corresponds to a combination of BRACH sub-channel index andBRACH sequence index.

According to an example embodiment, a direct association between a beamindex of a BFRS (CSI-RS, SS, or CSI-RS and SS) and a block index of aBRACH block is used to allow easy identification a block index from abeam index or vice versa. The beam index of a BFRS (CSI-RS, SS, orCSI-RS and SS) may be viewed as an absolute index of the BFRS beams,while the block index of a BRACH block may be viewed as an absoluteindex of the BRACH blocks. Such a direct CSI-RS to BRACH blockassociation (generally a one to one mapping) between beam indices andblock indices may be signaled by the access node by RRC signaling, forexample, or specified by a technical standard and stored in the devices.

FIG. 20C illustrates a table 2070 of an example direct associationbetween beam indices and block indices. Table 2070 presents beam indicesand block indices of the BRACH block configuration shown in FIG. 19.Table 2070 includes columns for BFRS index 2075 and BRACH index 2077.Values in BFRS index 2075 correspond to beam indices of BFRS beams andvalues in BRACH index 2077 correspond to block indices of BRACH blocks.Table 2070 presents a single example direct association between beamindices and block indices. Other direct associations are possible. Otherexample associations may include shifts, rotations, mathematicalmanipulations, and so on, of the indices.

Overall, for both direct and indirect associations, a UE may be able todetermine a BRACH block to transmit a preamble sequence to trigger beamfailure recovery based on a detected BFRS index. Similarly, at theaccess node, the access node is able to determine UE identity byanalyzing the preamble sequence, as well as determine the BFRS indexbased on the BRACH block index where the preamble sequence is received.

FIG. 21 illustrates second example BRACH resources 2100. As shown inFIG. 21, one or more BRACH resources is group into three timeopportunities, time opportunities 2105, 2107, and 2109. Each timeopportunity includes BRACH resources in the frequency domain (e.g., fourdifferent sub-channels) and the code domain (e.g., four different codesequences). Although BRACH resources 2100 are organized into three timeopportunities, with four sub-channels and four code sequences each, theexample embodiments presented herein are operable with other BRACHresource configurations. Therefore, the configuration presented in FIG.21 should not be construed as being limiting to the spirit or scope ofthe example embodiments.

As shown in FIG. 21, there are three time opportunities for each UE tosend a BRACH preamble. Each time opportunity may correspond to adifferent spatial direction in terms of beam direction of the WBRS. Foreach time opportunity, the UE may choose one of four sub-channels andone of four code sequences (A, B, C, and D) to transmit the BRACHpreamble. Therefore, the actual sub-channel index and actual preambleindex that a UE uses to transmit conveys 4 bits of information(corresponding to 16 different choices). The 4-bits of information maybe used by the UE to carry an intended beam index to the access node,for example. Therefore, there is a need for F*S*U=4*4*1=16, where F isthe number of sub-channels per UE, S is the number of code sequences perUE, and U is the number of UEs, to enable one UE to transmit whileconveying Log 2(F*S*U)=4 bits of information.

In order to enable K UEs to transmit at the same time while each UEtransmission is carrying 4-bits of information, more sub-channels may beneeded in the frequency domain or more code sequences are needed in thesequence domain, or both. However, the number of sub-channels and thenumber of code sequences are generally limited. When the number of UEs(K) is large, it is necessary for multiple UEs to share eithersub-channels or code sequences.

In the situation where multiple UEs are sharing code sequences, insteadof allocating BRACH resources (such as P1A, P1B, P1C, and P1D) to asingle UE, the access node may allocate a subset of the BRACH resources(e.g., P1A and P1B) to a first UE and another subset of the BRACHresources (e.g., P1C and P1D) to a second UE. Suppose then that each UEis still able to choose one of four sub-channels to transmit, then eachUE can choose one of eight (e.g., S=2 (halved due to sequence basedrestriction (SBR)) and F=4) resources to transmit. Therefore, thetransmission conveys Log 2(8)=3 bits of information. It is noted thatthe total number of resources (S*F*U) is still the same (16).

In the situation where multiple UEs are sharing sub-channels, instead ofallocating sub-channels (such as sub-channels 1, 2, 3, and 4) to asingle UE, the access node may allocate a subset of sub-channels (e.g.,sub-channels 1 and 2) to a first UE and another subset of sub-channels(e.g., sub-channels 3 and 4) to a second UE. Suppose then that each UEis still able to choose one of four code sequences to transmit, theneach UE can choose one of eight (e.g., F=2 (halved due to frequencybased restriction (FBR)) and S=₄) resources to transmit. Therefore, thetransmission conveys Log 2(8)=3 bits of information. It is noted thatthe total number of resources (S*F*U) is still the same (16). It isfurther noted that in this situation, the sequence P1A if detected onsub-channels 1 and 2 should be detected by the access node as thesequence P1A being sent by the first UE, while if sequence P1A isdetected on sub-channels 3 and 4, then the access node should determinethat the sequence P1A is sent by the second UE. In other words, todetermine UE identity, the access node needs to detect not only whatBRACH preamble is received, but where it is received.

It is also noted that a combination of the sharing presented above ispossible. In other words, the access node configures multiple UEs toshare the BRACH resources where:

-   -   Multiple UEs share the same sub-channel but differentiated by        different code sequences;    -   Multiple UEs share the same code sequences but differentiated by        different sub-channels; or    -   Multiple UEs are differentiated by different sub-channels and        different code sequences (i.e., not sharing).

It is noted that in FIG. 21, the same code sequence is used across allfour sub-channels of the different time opportunities (e.g., codesequence P1A is used in all four sub-channels). It is possible thatdifferent code sequences be used across the sub-channels of each timeopportunity. As an example, in a first sub-channel, code sequence P1A isused, in a second sub-channel, code sequence Q1A is used, in a thirdsub-channel, code sequence R1A is used, and in a fourth sub-channel,code sequence S1A is used.

FIG. 22A illustrates a flow diagram of example operations 2200 occurringin a UE initiating beam failure recovery. Operations 2200 may beindicative of operations occurring in a UE as the UE initiates beamfailure recovery.

Operations 2200 begin with the UE receiving beam index to BRACH indexassociations (block 2205). The beam index to BRACH index associationsmay be direct associations or indirect associations. The beam index toBRACH index associations may be received from an access node serving theUE. Alternatively, the beam index to BRACH index associations may beprogrammed into the UE. The UE detects a new beam and determines a beamindex of the new beam (block 2207). The new beam may be a replacementbeam for a failed beam. The UE determines a BRACH index (block 2209).The BRACH index may be determined from the beam index in accordance withthe beam index to BRACH index associations. The UE may optionally selecta BRACH preamble (block 2211). In a situation when the UE has beenconfigured with one or more BRACH preambles, the UE may select a BRACHpreamble from the plurality of BRACH preambles. Alternatively, the UEmay be configured with a single BRACH preamble but one or more codesequences with which to encode the BRACH preamble. In such a situation,the UE may optionally select a code sequence from the plurality of codesequences. The UE sends the BRACH preamble on a BRACH resourcecorresponding to the BRACH index (block 2213).

FIG. 22B illustrates a flow diagram of example operations 2250 occurringin an access node participating in beam failure recovery. Operations2250 may be indicative of operations occurring in an access node as theaccess node participates in beam failure recovery.

Operations 2250 begin with the access node sending beam index to BRACHindex associations (block 2255). The beam index to BRACH indexassociations may be direct associations or indirect associations. Thebeam index to BRACH index associations may be received from an accessnode serving the UE. Alternatively, the beam index to BRACH indexassociations may be programmed into the UE. The access node receives aBRACH preamble in a BRACH resource (block 2257). The access nodedetermines a beam index of a beam conveying a reference signaltransmitted by the access node (block 2259). The beam index may bedetermined from an index of the BRACH resource in accordance with thebeam index to BRACH index associations. The access node identifies theidentity of the UE (block 2261). The identity of the UE is determinedfrom the received BRACH preamble.

As related to resource allocation, the allocation may be performed atthe beginning when the UE establishes an active link with the accessnode. As an example, each UE may be assigned a unique recovery resource.In a first situation, a potentially unique beam recovery random accesschannel resource preamble in a random access channel region is assigned,with the random access channel region potentially being the same ordifferent from a random access channel region used for initial accesspurposes. In a second situation, a potentially unique set of REs in aregion are assigned. The REs may be identified by a unique combinationof code, time, or frequency resources.

If the random access channel region for beam failure recovery and therandom access channel region for initial access use different ororthogonal time or frequency resources, the same random access channelresource preamble may be used. As an example, if one UE is assigned afirst sequence to transmit in the random access channel region forinitial access, the UE may also use the same first sequence to transmitin the random access channel region for beam failure recovery.

If the random access channel region for beam failure recovery and therandom access channel region for initial access use the same randomaccess channel resource preamble, then a different scrambling code maybe used. As an example, if a UE is assigned a first sequence to transmitin the random access channel region for initial access, the UE may usethe same first sequence (but scrambled with a different scramblingsequence) to transmit in the random access channel region for beamfailure recovery. It is noted that the scrambling sequences fordifferent UEs may be the same or different. It is also noted that therandom access channel resource preamble sequences used in the randomaccess channel region for beam failure recovery and the random accesschannel region for initial access may be the orthogonal to each other.

If the random access channel region for beam failure recovery and therandom access channel region for initial access use the same oroverlapping time-frequency resources, the random access channel resourcepreamble sequences may be orthogonal to each other.

An example beam failure recovery procedure includes:

0a. An access node configures a UE with a unique preamble sequence touse in the random access channel region for beam failure recovery;

0b. The access node broadcast in a broadcast channel some resources(e.g., beam recovery reference signals, synchronization signals, and soon) to that the UE may use to make measurements in case of a beamfailure;

1. The UE monitors one or more downlink control channel; Upondetermining that a beam failure or loss has occurred, the UE mayinitialize the beam recovery procedure;

2. The UE makes downlink measurements:

-   -   On certain resources (e.g., beam recovery reference signals,        synchronization signals, and so on) to re-detect or        re-synchronize with downlink transmit beam(s) from the access        node (e.g., a downlink transmit beam with sufficient quality),        downlink receive beam(s) at the UE (e.g., a downlink receive        beam with sufficient quality), or to improve time or frequency        synchronization.    -   The location of the resources may be broadcast in advance by the        access node and may be periodically allocated in the time or        frequency domains;

3a. The UE transmits a preamble sequence in the random access channelregion for beam failure recovery. In a first situation, the UE transmitsits own unique preamble sequence in the random access channel region forbeam failure recovery (the random access channel region for beam failurerecovery may be non-orthogonal or orthogonal to the random accesschannel region for initial access in the time or frequency domains). Ina second situation, the UE may transmit a control or command in agrant-free manner on REs (this UE initiated grant-free transmission mayuse REs pre-allocated to the UE, for example). The uplink transmissionmay rely on time or frequency synchronization performed previously;

3b. The UE may transmit the downlink measurement results. As an example,the UE may transmit the best downlink transmit beam(s), e.g., beamindices. As an example, the UE may transmit the best downlink receivebeam(s), e.g., beam indices. As an example, the UE may transmit anassociated channel quality information, e.g., SINR, SNR, RSSI, RSRQ,RSRP, and so on. The UE may also transmit other information to theaccess node to help setup a new downlink control channel;

4. The access node receives the preamble sequence and associateddownlink measurement results. The access node may use the receivedinformation to establish a new downlink control channel from the accessnode to the UE; and

5. The access node may send control signaling to the UE using the newlyestablished downlink control channel.

FIG. 23 illustrates an example communication system 2300. In general,the system 2300 enables multiple wireless or wired users to transmit andreceive data and other content. The system 2300 may implement one ormore channel access methods, such as code division multiple access(CDMA), time division multiple access (TDMA), frequency divisionmultiple access (FDMA), orthogonal FDMA (OFDMA), single-carrier FDMA(SC-FDMA), or non-orthogonal multiple access (NOMA).

In this example, the communication system 2300 includes electronicdevices (ED) 2310 a-2310 c, radio access networks (RANs) 2320 a-2320 b,a core network 2330, a public switched telephone network (PSTN) 2340,the Internet 2350, and other networks 2360. While certain numbers ofthese components or elements are shown in FIG. 23, any number of thesecomponents or elements may be included in the system 2300.

The EDs 2310 a-2310 c are configured to operate and/or communicate inthe system 2300. For example, the EDs 2310 a-2310 c are configured totransmit and/or receive via wireless or wired communication channels.Each ED 2310 a-2310 c represents any suitable end user device and mayinclude such devices (or may be referred to) as a user equipment/device(UE), wireless transmit/receive unit (WTRU), mobile station, fixed ormobile subscriber unit, cellular telephone, personal digital assistant(PDA), smartphone, laptop, computer, touchpad, wireless sensor, orconsumer electronics device.

The RANs 2320 a-2320 b here include base stations 2370 a-2370 b,respectively. Each base station 2370 a-2370 b is configured towirelessly interface with one or more of the EDs 2310 a-2310 c to enableaccess to the core network 2330, the PSTN 2340, the Internet 2350,and/or the other networks 2360. For example, the base stations 2370a-2370 b may include (or be) one or more of several well-known devices,such as a base transceiver station (BTS), a NodeB (NodeB), an evolvedNodeB (eNodeB), a Home NodeB, a Home eNodeB, a site controller, anaccess point (AP), or a wireless router. The EDs 2310 a-2310 c areconfigured to interface and communicate with the Internet 2350 and mayaccess the core network 2330, the PSTN 2340, and/or the other networks2360.

In the embodiment shown in FIG. 23, the base station 2370 a forms partof the RAN 2320 a, which may include other base stations, elements,and/or devices. Also, the base station 2370 b forms part of the RAN 2320b, which may include other base stations, elements, and/or devices. Eachbase station 2370 a-2370 b operates to transmit and/or receive wirelesssignals within a particular geographic region or area, sometimesreferred to as a “cell.” In some embodiments, multiple-inputmultiple-output (MIMO) technology may be employed having multipletransceivers for each cell.

The base stations 2370 a-2370 b communicate with one or more of the EDs2310 a-2310 c over one or more air interfaces 2390 using wirelesscommunication links. The air interfaces 2390 may utilize any suitableradio access technology.

It is contemplated that the system 2300 may use multiple channel accessfunctionality, including such schemes as described above. In particularembodiments, the base stations and EDs implement LTE, LTE-A, and/orLTE-B. Of course, other multiple access schemes and wireless protocolsmay be utilized.

The RANs 2320 a-2320 b are in communication with the core network 2330to provide the EDs 2310 a-2310 c with voice, data, application, Voiceover Internet Protocol (VoIP), or other services. Understandably, theRANs 2320 a-2320 b and/or the core network 2330 may be in direct orindirect communication with one or more other RANs (not shown). The corenetwork 2330 may also serve as a gateway access for other networks (suchas the PSTN 2340, the Internet 2350, and the other networks 2360). Inaddition, some or all of the EDs 2310 a-2310 c may include functionalityfor communicating with different wireless networks over differentwireless links using different wireless technologies and/or protocols.Instead of wireless communication (or in addition thereto), the EDs maycommunicate via wired communication channels to a service provider orswitch (not shown), and to the Internet 2350.

Although FIG. 23 illustrates one example of a communication system,various changes may be made to FIG. 23. For example, the communicationsystem 2300 could include any number of EDs, base stations, networks, orother components in any suitable configuration.

FIGS. 24A and 24B illustrate example devices that may implement themethods and teachings according to this disclosure. In particular, FIG.24A illustrates an example ED 2410, and FIG. 24B illustrates an examplebase station 2470. These components could be used in the system 2300 orin any other suitable system.

As shown in FIG. 24A, the ED 2410 includes at least one processing unit2400. The processing unit 2400 implements various processing operationsof the ED 2410. For example, the processing unit 2400 could performsignal coding, data processing, power control, input/output processing,or any other functionality enabling the ED 2410 to operate in the system2300. The processing unit 2400 also supports the methods and teachingsdescribed in more detail above. Each processing unit 2400 includes anysuitable processing or computing device configured to perform one ormore operations. Each processing unit 2400 could, for example, include amicroprocessor, microcontroller, digital signal processor, fieldprogrammable gate array, or application specific integrated circuit.

The ED 2410 also includes at least one transceiver 2402. The transceiver2402 is configured to modulate data or other content for transmission byat least one antenna or NIC (Network Interface Controller) 2404. Thetransceiver 2402 is also configured to demodulate data or other contentreceived by the at least one antenna 2404. Each transceiver 2402includes any suitable structure for generating signals for wireless orwired transmission and/or processing signals received wirelessly or bywire. Each antenna 2404 includes any suitable structure for transmittingand/or receiving wireless or wired signals. One or multiple transceivers2402 could be used in the ED 2410, and one or multiple antennas 2404could be used in the ED 2410. Although shown as a single functionalunit, a transceiver 2402 could also be implemented using at least onetransmitter and at least one separate receiver.

The ED 2410 further includes one or more input/output devices 2406 orinterfaces (such as a wired interface to the Internet 2350). Theinput/output devices 2406 facilitate interaction with a user or otherdevices (network communications) in the network. Each input/outputdevice 2406 includes any suitable structure for providing information toor receiving/providing information from a user, such as a speaker,microphone, keypad, keyboard, display, or touch screen, includingnetwork interface communications.

In addition, the ED 2410 includes at least one memory 2408. The memory2408 stores instructions and data used, generated, or collected by theED 2410. For example, the memory 2408 could store software or firmwareinstructions executed by the processing unit(s) 2400 and data used toreduce or eliminate interference in incoming signals. Each memory 2408includes any suitable volatile and/or non-volatile storage and retrievaldevice(s). Any suitable type of memory may be used, such as randomaccess memory (RAM), read only memory (ROM), hard disk, optical disc,subscriber identity module (SIM) card, memory stick, secure digital (SD)memory card, and the like.

As shown in FIG. 24B, the base station 2470 includes at least oneprocessing unit 2450, at least one transceiver 2452, which includesfunctionality for a transmitter and a receiver, one or more antennas2456, at least one memory 2458, and one or more input/output devices orinterfaces 2466. A scheduler, which would be understood by one skilledin the art, is coupled to the processing unit 2450. The scheduler couldbe included within or operated separately from the base station 2470.The processing unit 2450 implements various processing operations of thebase station 2470, such as signal coding, data processing, powercontrol, input/output processing, or any other functionality. Theprocessing unit 2450 can also support the methods and teachingsdescribed in more detail above. Each processing unit 2450 includes anysuitable processing or computing device configured to perform one ormore operations. Each processing unit 2450 could, for example, include amicroprocessor, microcontroller, digital signal processor, fieldprogrammable gate array, or application specific integrated circuit.

Each transceiver 2452 includes any suitable structure for generatingsignals for wireless or wired transmission to one or more EDs or otherdevices. Each transceiver 2452 further includes any suitable structurefor processing signals received wirelessly or by wire from one or moreEDs or other devices. Although shown combined as a transceiver 2452, atransmitter and a receiver could be separate components. Each antenna2456 includes any suitable structure for transmitting and/or receivingwireless or wired signals. While a common antenna 2456 is shown here asbeing coupled to the transceiver 2452, one or more antennas 2456 couldbe coupled to the transceiver(s) 2452, allowing separate antennas 2456to be coupled to the transmitter and the receiver if equipped asseparate components. Each memory 2458 includes any suitable volatileand/or non-volatile storage and retrieval device(s). Each input/outputdevice 2466 facilitates interaction with a user or other devices(network communications) in the network. Each input/output device 2466includes any suitable structure for providing information to orreceiving/providing information from a user, including network interfacecommunications.

FIG. 25 is a block diagram of a computing system 2500 that may be usedfor implementing the devices and methods disclosed herein. For example,the computing system can be any entity of UE, access network (AN),mobility management (MM), session management (SM), user plane gateway(UPGW), and/or access stratum (AS). Specific devices may utilize all ofthe components shown or only a subset of the components, and levels ofintegration may vary from device to device. Furthermore, a device maycontain multiple instances of a component, such as multiple processingunits, processors, memories, transmitters, receivers, etc. The computingsystem 2500 includes a processing unit 2502. The processing unitincludes a central processing unit (CPU) 2514, memory 2508, and mayfurther include a mass storage device 2504, a video adapter 2510, and anI/O interface 2512 connected to a bus 2520.

The bus 2520 may be one or more of any type of several bus architecturesincluding a memory bus or memory controller, a peripheral bus, or avideo bus. The CPU 2514 may comprise any type of electronic dataprocessor. The memory 2508 may comprise any type of non-transitorysystem memory such as static random access memory (SRAM), dynamic randomaccess memory (DRAM), synchronous DRAM (SDRAM), read-only memory (ROM),or a combination thereof. In an embodiment, the memory 2508 may includeROM for use at boot-up, and DRAM for program and data storage for usewhile executing programs.

The mass storage 2504 may comprise any type of non-transitory storagedevice configured to store data, programs, and other information and tomake the data, programs, and other information accessible via the bus2520. The mass storage 2504 may comprise, for example, one or more of asolid state drive, hard disk drive, a magnetic disk drive, or an opticaldisk drive.

The video adapter 2510 and the I/O interface 2512 provide interfaces tocouple external input and output devices to the processing unit 2502. Asillustrated, examples of input and output devices include a display 2518coupled to the video adapter 2510 and a mouse/keyboard/printer 2516coupled to the I/O interface 2512. Other devices may be coupled to theprocessing unit 2502, and additional or fewer interface cards may beutilized. For example, a serial interface such as Universal Serial Bus(USB) (not shown) may be used to provide an interface for an externaldevice.

The processing unit 2502 also includes one or more network interfaces2506, which may comprise wired links, such as an Ethernet cable, and/orwireless links to access nodes or different networks. The networkinterfaces 2506 allow the processing unit 2502 to communicate withremote units via the networks. For example, the network interfaces 2506may provide wireless communication via one or more transmitters/transmitantennas and one or more receivers/receive antennas. In an embodiment,the processing unit 2502 is coupled to a local-area network 2522 or awide-area network for data processing and communications with remotedevices, such as other processing units, the Internet, or remote storagefacilities.

It should be appreciated that one or more steps of the embodimentmethods provided herein may be performed by corresponding units ormodules. For example, a signal may be transmitted by a transmitting unitor a transmitting module. A signal may be received by a receiving unitor a receiving module. A signal may be processed by a processing unit ora processing module. Other steps may be performed by a determiningunit/module, a monitoring unit/module, an identifying unit/module, asetting up unit/module, and/or a configuring unit/module. The respectiveunits/modules may be hardware, software, or a combination thereof. Forinstance, one or more of the units/modules may be an integrated circuit,such as field programmable gate arrays (FPGAs) or application-specificintegrated circuits (ASICs).

Although the present disclosure and its advantages have been describedin detail, it should be understood that various changes, substitutionsand alterations can be made herein without departing from the spirit andscope of the disclosure as defined by the appended claims.

1. A method for operating a user equipment (UE), the method comprising:monitoring, by the UE, a first set of reference signals of a firstreference signal type and a second set of reference signals of a secondreference signal type; identifying, by the UE, a second reference signalfrom the second set of reference signals as a candidate beam;identifying, by the UE, a first reference signal of the first set ofreference signals that is quasi collocated with the candidate beam; andtransmitting, by the UE, a preamble sequence on a random access channelresource that is associated with the first reference signal.
 2. Themethod of claim 1, wherein the first set of reference signals comprisessynchronization signals (SSs), and wherein the second set of referencesignals comprises channel state information reference signals (CSI-RSs).3. The method of claim 1, wherein identifying the second referencesignal from the second set of reference signals as a candidate beamcomprises determining that a signal quality of the second referencesignal meets a threshold.
 4. The method of claim 1, further comprisingreceiving, by the UE, information about the first set of referencesignals and the second set of reference signals in at least one of aradio resource control (RRC) message, a medium access control (MAC)control element (CE) (MAC-CE) message, or a downlink control indicator(DCI) message.
 5. The method of claim 1, further comprising receiving,by the UE, information about the quasi collocated relationship betweenthe first set of reference signals and the second set of referencesignals in at least one of a radio resource control (RRC) message, amedium access control (MAC) control element (CE) (MAC-CE) message, or adownlink control indicator (DCI) message.
 6. The method of claim 1,further comprising receiving, by the UE, at least one of informationabout an association between preamble sequences and the first set ofreference signals, or information about an association between randomaccess channel resources and the first set of reference signals.
 7. Themethod of claim 6, wherein information about the association between afirst random access channel resource and the first set of referencesignals comprises at least one of time location information of the firstrandom access channel resource, or frequency location information of thefirst random access channel resource.
 8. The method of claim 1, whereinthe random access channel resource is unique to the UE.
 9. A method foroperating an access node, the method comprising: sending, by the accessnode, information about a quasi collocated relationship between a firstset of reference signals of a first reference signal type and a secondset of reference signals of a second reference signal type; sending, bythe access node, the first set of reference signals and the second setof reference signals; and receiving, by the access node from a userequipment (UE), a preamble sequence associated with a reference signalof the first set of reference signals on a random access channelresource, wherein the preamble sequence identifies a candidate beam. 10.The method of claim 9, further comprising assigning, by the access node,the random access channel resource or the preamble sequence to the UE.11. The method of claim 9, wherein the first set of reference signals ofthe first reference signal type comprises a set of synchronizationsignals (SSs), and wherein the second set of reference signals of thesecond reference signal type comprises a set of channel stateinformation reference signals (CSI-RSs).
 12. The method of claim 9,wherein the information is sent in at least one of a radio resourcecontrol (RRC) message, a medium access control (MAC) control element(CE) (MAC-CE) message, or a downlink control indicator (DCI) message.13. A user equipment (UE) comprising: a non-transitory memory storagecomprising instructions; and one or more processors in communicationwith the memory storage, wherein the one or more processors execute theinstructions to: monitor a first set of reference signals of a firstreference signal type and a second set of reference signals of a secondreference signal type, identify a second reference signal from thesecond set of reference signals as a candidate beam, identify a firstreference signal of the first set of reference signals that is quasicollocated with the candidate beam, and transmit a preamble sequence ona random access channel resource that is associated with the firstreference signal.
 14. The UE of claim 13, wherein the first set ofreference signals comprises synchronization signals (SSs), and whereinthe second set of reference signals comprises channel state informationreference signals (CSI-RSs).
 15. The UE of claim 13, wherein the one ormore processors further execute instructions to receive informationabout the first set of reference signals and the second set of referencesignals in at least one of a radio resource control (RRC) message, amedium access control (MAC) control element (CE) (MAC-CE) message, or adownlink control indicator (DCI) message.
 16. The UE of claim 13,wherein the one or more processors further execute instructions toreceive at least one of information about the association betweenpreamble sequences and the first set of reference signals, orinformation about the association between random access channelresources and the first set of reference signals.
 17. The UE of claim16, wherein information about the association between a first randomaccess channel resource and the first set of reference signals comprisesat least one of time location information of the first random accesschannel resource, or frequency location information of the first randomaccess channel resource.
 18. An access node comprising: a non-transitorymemory storage comprising instructions; and one or more processors incommunication with the memory storage, wherein the one or moreprocessors execute the instructions to: send information about a quasicollocated relationship between a first set of reference signals of afirst reference signal type and a second set of reference signals of asecond reference signal type, send the first set of reference signalsand the second set of reference signals, and receive, from a userequipment (UE), a preamble sequence associated with a reference signalon the first set of reference signals on a random access channelresource, wherein the preamble sequence identifies a candidate beam. 19.The access node of claim 18, wherein the one or more processors furtherexecute instructions to assign the random access channel resource or thepreamble sequence to the UE.
 20. The access node of claim 18, whereinthe information is sent in at least one of a radio resource control(RRC) message, a medium access control (MAC) control element (CE)(MAC-CE) message, or a downlink control indicator (DCI) message.
 21. Themethod of claim 1, where the first reference signal and the candidatebeam are transmitted using a same type of spatial transmitter, or can bereceived using a same type of spatial receiver.
 22. The method of claim1, wherein the preamble sequence is associated with the first referencesignal.
 23. The access node of claim 18, wherein the first set ofreference signals of the first reference signal type comprises a set ofsynchronization signals (SSs), and wherein the second set of referencesignals of the second reference signal type comprises a set of channelstate information reference signals (CSI-RSs).